Thermal

Thermal (pronounced thur-muhl)

(1) Of, relating to, or caused by heat or temperature (also thermic); of, relating to, or of the nature of thermae.

(2) As (both noun and adjective) thermal blanket or thermal underwear (as a noun, always referred to in the plural (thermals) even if describing a single item), items designed to aid in or promote the retention of body heat.

(3) In meteorology, a column of rising air caused by local unequal heating by the sun of the land surface, especially such a current when not producing a cloud; widely used in aviation and of especial importance in gliding, a borrowing of the techniques used by birds. The air usually rises until it is in equilibrium with the surrounding atmosphere.

(4) In stonemasonry, a rough finish created with a blowtorch.

1756: From the French thermal (buffon), from the New Latin thermalis, from the Ancient Greek θέρμη (thérmē) (heat; feverish heat), from the primitive Indo-European gwher (to heat, warm).  The construct was therm + -al (from the Latin adjectival suffix -ālis, or the French, Middle French & Old French -el, -al; used mostly but not exclusively with word of Latin origin).  The sense of "having to do with heat" is first recorded 1837; the noun meaning "rising current of relatively warm air" was first noted in 1933 in the context of aviation.  Geothermal first used in 1875; hydrothermal in 1855, exothermal in 1874; athermanous in 1839, hyperthermia in 1878, isotherm in 1850, endothermic in 1869 (1947 as applied in biology) and thermometer as early as the 1597 although the most familiar (pre-digital) version with mercury encased in glass, was invented by Fahrenheit in 1714.  Thermal is adjective in the singular and a noun in the singular or plural, thermally is the adverb.  The most common derivations are the adjectives hyperthermal and the adverb hyperthermally but in engineering and science there’s also therm, therma, thermacogenesis, thermae, aerothermal, thermometric, thermometrical & thermaesthesia.  Thermal is a noun, verb & adjective; the noun plural is thermals.

Thermal Reactive Nail Polish

Thermal reactive nail polishes change color depending on both body and ambient temperature.  Nail polish is especially suitable for thermal reactivity because the extremities of the body (fingertips, toes, ears & nose) vary in temperature much more than parts closer to the core.  Usefully, they work with even the thickest base and top-coats which affords additional protection for the thermal-reactive chemicals, the color-changing properties affected not at all if multiple coats are applied.

The process is entirely heat-dependent and thus constantly variable.  In this example the reaction produces purple in reaction to cold and aqua to warmth; because the temperature of the nail greatly can vary between base and tip, the ombré effect (colors blending from one hue to another) will fluctuate.  The chemical reaction does rely on the top coat being fully dry and, depending on manufacturer, this can take up to an hour.  The special properties don't last forever but, if correctly sealed, stored in a dark place and not exposed to extremes of heat and cold, the liquid will for months continue to be reactive.

Chemically, the thermal reactivity works because the polish is infused with a leuco (“white” in Ancient Greek) dye, the word a little misleading in this context because leuco dyes have two forms: one clear, the other colored. The reversible transition between the two colors may be caused by heat (thermochromism), light (photochromism) or pH (halochromism) and in other (often industrial) applications, it’s possible irreversibly to change colors, usually from a redox reaction.

For thermal nail polish, the dye comes packaged in tiny spheres called microcapsules, each only 1-10 microns in diameter but containing three chemicals: (1) leuco dye which changes color reversibly, the color depending on the dye which, when combined with a proton or hydrogen ion, becomes colorless.  (2) A weak acid which acts as a catalyst, donating the hydrogen ion.  (3) A solvent which induces a color change at a desired temperature.  When cool, the solvent solidifies, the hydrogen remaining stuck to the acid and thus not interacting with the colored dye.  When hot, the solvent melts, the weak acid dissociates, the hydrogen ion binds to the dye, and the dye is colorless.  The temperature-shift range is about 5ºF (3ºC).

Those not content with the commercially available color combinations easily can brew their own thermal reactive polish.  Leuco dyes are available in many colors and come as a powder, slurry, epoxy, or water-based ink but only the powder is suitable and the transition range should hover 88ºF (31ºC) because nails are cooler than body temperature.  The choice of polish color dictates the result.  A white polish will produce a pastel result, a pale color will switch between the original and the combination of the leuco and the color so a mix of pink polish and a blue leuco dye yields a color shift from pink to purple.

To mix, place 1-2 small ball bearings in empty nail polish bottle and fill with polish to about half-way.  Add leuco dye to achieve desired color (about ⅛ teaspoon) and, if ambient temperature is high, chill the bottle to see result.  When mixing, cap bottle and gently roll it; do not shake because this will cause cavitation, the formation of air bubbles which impede the blending.  If the polish is too thick, add a few drops of nail polish thinner or clear top-coat but never acetone or other nail polisher remover because these chemicals ruin the mix.  Glitter or holo may be added according to taste.

Lindsay Lohan on skis in fuchsia, Falling for Christmas (Netflix (2022)), her thermal base layer unknown.

When skiing or mountain climbing, thermal underwear is usually the ideal choice for what is called the “thermal base layer”, a combination which consists usually of a top and a pair of leggings.  Outer layers of ski clothing perform better when a thermal base layer is worn because the moisture from the body rapidly is wicked away in a capillary action, permitting the breathable fabrics of the outer garments more efficiently to dissipate the moisture more efficiently.  It’s often thought the only purpose of thermal underwear is to increase body temperature but it’s the symbiosis between the thermal base layer and the outer coverings which regulate body temperature, maintaining comfort in both colder and warmer conditions.  By volume, most thermal underwear is made from Polyester (a type of plastic called polypropylene), often augmented with Lycra and all these garments are produced in a very tight weave which delivers good thermal qualities and what the manufacturers call a high “breathability factor”.

Also used is fine wool which, being a natural fibre, is preferred by many and it does posses the virtues of offering both comfort and efficient thermal qualities.  The choice between the types of construction is less about specific differences in thermal performance than how one’s skin reacts and sometimes this is something which can be judged only after prolonged exposure in a variety of temperatures.  All types are available in both short and long (sleeves & legs) versions and because the material is so thin, the longer cuts intrude not at all upon the fit of gloves and boots and the choice is again one of personal preference although, in extreme conditions, the full-versions should always at least be packed.

Fecund & Fertile

Fecund (pronounced fuh-khunt, fee-kuhnd or fek-uhnd)

(1) Producing or capable of producing offspring, fruit, vegetation, etc in abundance; prolific; fruitful.

(2) Figuratively, highly productive or creative intellectually; innovative.

Circa 1525: From the mid-fifteenth century Middle English fecounde from the Middle French fecund, from the Old French fecund & fecont (fruitful), from the Latin fēcundus (fruitful, fertile, productive; rich, abundant (and related to the Latin fētus (offspring) and fēmina (“woman”)), from fe-kwondo-, an adjectival suffixed form of the primitive Indo-European root dhei or dhe- (to suck, suckle), other derivatives meaning also “produce” & “yield”.  Fē in this case wasn’t a prefix but a link to fetus whereas -cundus was the adjectival suffix.  It replaced the late Middle English fecounde.  The spelling fecund was one of the “Latinizing” revisions to spelling which was part of the framework of early Modern English, (more or less) standardizing use and replacing the Middle English forms fecond, fecound & fecounde.  The Latin root itself proved fecund; from it came also felare (to suck), femina (woman (literally “she who suckles”)); felix (happy, auspicious, fruitful), fetus (offspring, pregnancy); fenum (hay (which seems literally to have meant “produce”)) and probably filia (daughter) & filius (son), assimilated from felios (originally “a suckling”).  The noun fecundity emerged in the early fifteenth century and was from the Latin fecunditatem (nominative fecunditas) (fruitfulness, fertility), from fecundus (fruitful, fertile).  The old spelling fœcund is obsolete.  Fecund is an adjective and fecundity & fecundation are nouns; the noun plural is fecundities.

In his A Dictionary of Modern English Usage (1926), Henry Fowler (1858–1933) noted without comment the shift in popular pronunciation but took the opportunity to cite the phrase of a literary critic (not a breed of which he much approved) who compared the words of HG Wells (1866-1946) & Horace Walpole (1717–1797): “The fecund Walpole and the facund Wells”.  The critic, Henry Fowler noted: “fished up the archaic facund for the sake of the play on words”.  Never much impressed by flashy displays of what he called a “pride of knowledge”, his objection here was that there was nothing in the sentence to give readers any idea of the change in meaning caused by the substituted vowel.  Both were from Latin adjectives, fēcundus (prolific) and facundus (elegant).

Fertile (pronounced fur-tl or fur-tahyl (mostly UK RP))

(1) Of land, bearing, producing, or capable of producing vegetation, crops etc, abundantly; prolific.

(2) Of living creatures, bearing or capable of bearing offspring; Capable of growth or development.

(3) Abundantly productive.

(4) Conducive to productiveness.

(5) In biology, fertilized, as an egg or ovum; fecundated; capable of developing past the egg stage.

(6) In botany, capable of producing sexual reproductive structures; capable of causing fertilization, as an anther with fully developed pollen; having spore-bearing organs, as a frond.

(7) In physics (of a nuclide) capable of being transmuted into a fissile nuclide by irradiation with neutrons (Uranium 238 and thorium 232 are fertile nuclides); (a substance not itself fissile, but able to be converted into a fissile material by irradiation in a reactor).

(8) Figuratively, of the imagination, energy etc, active, productive, prolific.

1425–1475: From the Late Middle English fertil (bearing or producing abundantly), from the Old French fertile or the Latin fertilis (bearing in abundance, fruitful, productive), from ferō (I bear, carry) and .akin to ferre (to bear), from the primitive Indo-European root bher (to carry (also “to bear children”)).  The verb fertilize dates from the 1640s in the sense of “make fertile” although the use in biology meaning “unite with an egg cell” seems not to have been used until 1859 and use didn’t become widespread for another fifteen years.  The noun fertility emerged in the mid-fifteenth century, from the earlier fertilite, from the Old French fertilité, from the Latin fertilitatem (nominative fertilitas) (fruitfulness, fertility), from fertilis (fruitful, productive).  Dating from the 1660s, the noun fertilizer was initially specific to the technical literature associated with agriculture in the sense of “something that fertilizes (land)”, and was an agent noun from the verb fertilize.  In polite society, fertilizer was adopted as euphemism for “manure” (and certainly “shit”), use documented since 1846.  The noun fertilization is attested since 1857 and was a noun of action from fertilize; it was either a creation of the English-speaking world or a borrowing of the Modern French fertilisation.  The common antonyms are barren, infertile and sterile.  Fertile is an adjective, fertility, fertilisation & fertileness are nouns, fertilize fertilized & fertilizing are verbs.  Technical terms like sub-fertile, non-fertile etc are coined as required.

The term “Fertile Crescent” was coined in 1914 was coined by US-born University of Chicago archaeologist James Breasted (1865-1935); it referred to the strip of fertile land (in the shape of an irregular crescent) described the stretching from present-day Iraq through eastern Turkey and down the Syrian and Israeli coasts.  The significance of the area in human history was it was here more than ten-thousand years ago that settlements began the practice of structured, seasonal agriculture.  The Middle English synonym childing is long obsolete but the more modern term “at risk” (of falling pregnant) survives for certain statistical purposes and was once part of the construct of a “legal fiction” in which the age at which women were presumed to be able to conceive was set as high as 65; advances in medical technology have affected this.

The difference

So often are “fecund” & “fertile” used interchangeably that there may be case to be made that in general use they are practically synonyms.  However, the use is slanted because fertile is a common word and fecund is rare; it’s the use of fertile when, strictly speaking, fecund is correct which is the frequent practice.  Technically, the two have distinct meanings although there is some overlap and agriculture is a fine case-study: Fertile specifically refers to soil rich in nutrients and able to support the growth of plants.  Fecund can refer to soil capable of supporting plant growth but it has the additional layer of describing something capable of producing an abundance of offspring or new growth.  This can refer to animals, humans, bacteria or (figuratively), ideas.  Used interchangeably, expect between specialists who need to differentiate, this linguistic swapping probably doesn’t cause many misunderstandings because the context of conversations will tend to make the meaning clear and for most of use, the distinction between a soil capable of growing plants and one doing so prolifically is tiresomely technical.  Still, as a rule of thumb, fertile can be thought of as meaning “able to support the growth of offspring or produce” while fecund implies “producing either in healthy volumes”.

Ultimate fecundity: Fast breeding

Although there are differences in meaning, fertile and fecund tend to be used interchangeably, especially in agriculture.  As adjectives, the difference is that fecund means highly fertile whereas fertile is the positive side of the fertile/infertile binary; capable of producing crops or offspring.  Fecundity may thus be thought a measure of the extent to which fertility is realised.  In nuclear physics, fertile material is that which, while not itself fissile (ie fissionable by thermal neutrons) is able to be converted into fissile material by irradiation in a reactor.  Three basic fertile materials exist: thorium-232, uranium-234 & uranium-238 and when these materials capture neutrons, respectively they are converted into uranium-233, uranium-235 & fissile plutonium-239.  Artificial isotopes formed in the reactor which can be converted into fissile material by one neutron capture include plutonium-238 and plutonium-240 which convert respectively into plutonium-239 & plutonium-241.

Obviously fertile and recently fecund.  In July 2023 Lindsay Lohan announced the birth of her first child.

Further along the scale are the actinides which demand more than one neutron capture before arriving at an isotope which is both fissile and long-lived enough to capture another neutron and reason fission instead of decaying.  These strings include (1) plutonium-242 to americium-243 to curium-244 to curium-245, (2) uranium-236 to neptunium-237 to plutonium-238 to plutonium-239 and (3) americium-241 to curium-242 to curium-243 (or, more likely, curium-242 decays to plutonium-238, which also requires one additional neutron to reach a fissile nuclide).  Since these require a total of three or four thermal neutrons eventually to fission, and a thermal neutron fission generates typically only two to three neutrons, these nuclides represent a net loss of neutrons although, in a fast reactor, they may require fewer neutrons to achieve fission, as well as producing more neutrons when they do.

Fast breeder (fusion) reactors have existed in labs for decades but, because of the need to contain sustainably very high temperatures, the challenge has always been to build something which (1) produces more energy than it consumes and (2) does so indefinitely.  On paper (and physicists admit the design is now so well understood a conceptual diagram can be sketched on a sheet in minutes) the science and engineering works so all that stands in the way is economics.  The lure of the fast breeder reactor is that, theoretically endlessly, one can produce more fissile material than it consumes (they're constructed using fertile material either wrapped around the core or encased in fuel rods).  Because plutonium-238, plutonium-240 and plutonium-242 are fertile, their accumulation is more manageable than that produced in conventional thermal reactors.  On planet Earth, the economics remain un-compelling, practical application of the technology having been thirty years off since the mid-1950s.  One proposal however transcends economics because it solves an otherwise insoluble problem.  If a facility for the manufacture of fissile material for spacecraft nuclear propulsion could be located on a space facility located at a point beyond the gravitational pull of Earth, it would be safe both to transport fertile materials to the facility and there manufacture fissile material which could provide the energy required for space exploration.

Vantablack

Vantablack (pronounced van-tah-blak)

(1) A black material which absorbs 99.965% of light reaching its surface.

(2) A shade of black of extraordinary blackness.

(3) Used loosely, of or pertaining to something very black.   

2014: A coining in Modern English, the construct being Vanta (the acronym for Vertically Aligned NanoTube Arrays) + black.  Black (in the sense of the color (absorbing all light and reflecting none; dark and hueless)) was from the Middle English blak, black & blake, from the Old English blæc (black, dark (also “ink”), from the Proto-West Germanic blak, from the Proto-Germanic blakaz (burnt).  Related were the Dutch blaken (to burn), the Low German blak & black (blackness, black paint (black) ink) and the Old High German blah (black), possibly from the primitive Indo-European bhleg- (to burn, shine).

Vantablack is built from clusters of vertical nanotubes on a substrate using a modified chemical vapour deposition process (CVD).  When light strikes Vantablack, instead of reflecting back and thus being visible, it becomes trapped, bouncing among the tubes until absorbed, dissipating into heat.  The densities are impressive for physical stuff; each square centimetre contains about a billion nanotubes.  Industrially, it’s an improvement over previous products because it can be created at 750°f (400°c) whereas an earlier substance, developed by NASA, demanded a 1380°f (750°c) environment.  However, in manufacturing, this is expensive and, Vantablack can be grown only on materials capable of enduring this temperature, further limiting commercial application.  Despite this Vantablack is a functional improvement which also offers better thermal stability and a greater resistance to mechanical vibration.  First developed in the UK’s National Physical Laboratory, trademark is held by Surrey NanoSystems.  The blackest known material ever in earthly existence, Vantablack is used to improve the performance of both ground and space-based cameras, improve heat-absorption in solar arrays and prevent stray light entering telescopes.  The military apply it to thermal camouflage because if used to coat 3D objects, they appear visually flat “black holes” without any shape or depth.

Potential LVBD customer.  Lindsay Lohan and the quest for the perfect LBD.

Surrey Nanosystems in 2016 granted Sir Anish Kapoor (an Indian-born UK British sculptor), the sole licence exclusively to use Vantablack for all “artistic purposes”, meaning no other artist could produce work using the material.  The exclusivity clause attracted much criticism from other artists who claimed it was absurd to suggest an individual could enjoy sole rights to a color.  While that might have been the consequence, what Surry did was licence the use of a commercial product for certain limited purposes, something hardly unusual in industry.  What triggered the controversy was that it involved restricted artists producing their product for some commercial gain; there is nothing to prevent anyone creating an artwork using Vantablack; it just can’t be exhibited or sold and must exist only for personal enjoyment.  Some artists actually responded by producing and trade-making certain products and making them freely available to any artist except Sir Anish; he was banned.  Legal commentators and philosophers have about the written about what is clearly a restraint of trade and the consensus seems to be Surrey is on sound legal ground but there should be a debate about whether intellectual property in the matter of the use of materials should be extended to art.

Entropy

Entropy (pronounced en-truh-pee)

(1) In thermodynamics,  the capacity factor for thermal energy that is hidden with respect to temperature; an expression of the dispersal of energy; a measure of the energy is spread out in a process, or how widely spread out it becomes, at a specific temperature.

(2) In thermodynamics (on a macroscopic scale), a function of thermodynamic variables, as temperature, pressure, or composition, that is a measure of the energy not available for work during a thermodynamic process (a closed system evolves toward a state of maximum entropy).

(3) In statistical mechanics, a measure of the randomness of the microscopic constituents of a thermodynamic system (symbol=S).  Technically, a statistical measure of the disorder of a closed system expressed by S = k log P + c where P is the probability that a particular state of the system exists, k is the Boltzmann constant, and c is another constant).  Expressed as joules per kelvin, it's essentially a measure of the information and noise present in a signal.

(4) In data transmission and information theory, an expression of specific efficiency, a measure of the loss of information in a transmitted signal or message.

(5) In cosmology, a hypothetical tendency for the universe to attain a state of maximum homogeneity in which all matter is at a uniform temperature (heat death).

(6) In political science, a doctrine of inevitable social decline and degeneration; the tendency of a system that is left to itself to descend into chaos (this definition widely used literally and figuratively in many fields).

(7) In modeling theory and applied modeling, a lack of pattern or organization; a state of marked disorder; a measure of the disorder present in a system.

1867: From the German Entropie, coined in 1865 by German physicist and mathematician Rudolph Clausius (1822–1888) by analogy with Energie (energy), replacing the root of Ancient Greek ἔργον (érgon) (work) by the Ancient Greek τροπή (tropḗ) (transformation).  The Ancient Greek ἐντροπία (entropía) (a turning towards) is from energie, the construct being en (in) + trope (a turning, a transformation) from the primitive Indo-European trep (to turn).  Rudolph Clausius had for years been working on his theories before he coined the word Entropie to describe what he had been calling "the transformational content of the body."  The new word encapsulated the second law of thermodynamics as "the entropy of the universe tends toward a maximum" but Clausius thought the concept better illustrated by the mysterious disgregation (an series of equations explaining dissolution at the particle level), another of his coinings which never caught on in the same way.  Entropy & entropology are nouns, entropic is an adjective and entropically is an adverb; the noun plural is entropes.  The synonym entropia is an internationalism rarely used in English.

Entropy describes uncertainty or disorder in a system and, in casual use, refers to degradation or disorder in any situation, or to chaos, disorganization, or randomness in general.  In a technical sense, it is the gradual breakdown of energy and matter in the universe and is an important part of several theories which postulate how the universe will end.  The laws of thermodynamics describe the relationships between thermal energy, or heat, and other forms of energy, and how energy affects matter.  The First Law of Thermodynamics states that energy cannot be created or destroyed; the total quantity of energy in the universe stays the same. The Second Law of Thermodynamics is about the quality of energy.  It states that as energy is transferred or transformed, more and more of it is wasted. The second law also states there is a natural tendency of any isolated system to degenerate into a more disordered state; at a microscopic level, if a system is isolated, any natural process in that system progresses in the direction of increasing disorder, or entropy, of the system.  The second law also predicts the end of the universe, implying the universe will end when everything becomes the same temperature. This is the ultimate level of entropy; if everything is the same temperature, nothing can happen and energy can manifest only as the random motion of atoms and molecules.  Time would stop immediately after the point at which, for the first time since the point at which the big bang happened, everything was happening at the same time.

Lindsay Lohan and her lawyer in court, Los Angeles, December 2011.

The term entropology is a portmanteau word (the construct of the blend being entrop(y) +‎ (anthrop)ology) which was 1955 coined by the French anthropologist Claude Lévi-Strauss (1908–2009) whose theories and models even today continue to underpin some of the framework of structural anthropology, the debt to him acknowledged by structuralists in many fields and apart from all else, in the social sciences, words like entropology are much admired.  It first appeared in his book Tristes Tropiques (Sad Tropics (1955)) a text itself structurally interesting, being in part travelogue, research paper and memoir, interspersed with philosophical musing on music, literature, history, architecture and sociology; these days it’d be called post-modern.  The essence of entropology is that the transformative path of human cultures (the sometimes separate, sometime parallel notion of “civilization” seemed not to trouble Lévi-Strauss) is inherently corrosive & disruptive.  It seemed a grim thesis but it must be admitted that by 1955, there was plenty of evidence to support his view.

A probably inaccurate representation of nothing.

The idea of nothing, in a universal sense in which literally nothing (energy, matter, space or time) exists is difficult to imagine, imaginable presumably only as infinite blackness although even that would seem to imply the spatial.  That nothingness is perhaps impossible to imagine or visualize doesn’t however prove it’s impossible but the mere fact matter, energy and time now exist in space does imply that because, were there ever nothing, it’s a challenge to explain how anything could have, from nothing, come into existence.  Despite that, it would be interesting if cosmologists could attempt to describe the mathematics of a model which would describe what conditions would have to prevail in order for there truly to be nothing.  That may or may not be possible but might be an interesting basis from which to work for those trying to explain things like dark matter & dark energy, either or both of which also may or may not exist.  Working with the existing universe seems not to be helpful in developing theories about the nature of all this supposedly missing (or invisible) matter and energy whereas were one, instead of working backwards as it were, instead to start with nothing and then work out how to add what seems to be missing (while remaining still not visible), the result might be interesting.

Trunk

Trunk (pronounced truhngk)

(1) The main stem of a tree, as distinct from the branches (limbs) and roots (also as bole; tree trunk).

(2) Of, relating to or noting a main channel or line, as of a railroad, waterway or something which assumes a similar shape (topographically).

(3) A large, sturdy box or chest for holding or transporting clothes, personal effects or other articles.  Such trunks usually have a hinged (sometimes domed) lid and handles at each end, provided because such is the size & weight, it takes at least two to carry one when loaded.

(4) A compartment, most often in the rear coachwork of an automobile, in which luggage, a spare tire, and other articles may be kept (a “boot” in the UK and certain other places in the English-speaking world and a “dicky” in India and elsewhere in South Asia).

(5) A storage compartment fitted behind the seat of a motorcycle and known also as a top-ox or top-case (as distinct from a “pannier” or “saddlebag” which is fitted at the side (usually in pairs), below the level of the seat).

(6) In anatomy, the body of a person or an animal excluding the head and limbs (the torso).

(7) In pathology, the main body of an artery, nerve, or the like, as distinct from its branches.

(8) In ichthyology, that part of a fish between the head and anus.

(9) In engineering and architecture, a name for a conduit, shaft, duct, channel or chute etc, used variously for airflow (thermal or blown), water, coal, grain etc.

(10) In steam engines, a large pipe forming the piston rod of a steam engine, of sufficient diameter to allow one end of the connecting rod to be attached to the crank, and the other end to pass within the pipe directly to the piston, thus making the engine more compact.

(11) In extractive mining, a flume or sluice in which ores are separated from the slimes in which they are contained.

(12) In architecture, the dado or die of a pedestal.

(13) In architecture, the part of a pilaster between the base and capital, corresponding to the shaft of a column.

(14) In hydrology, the main channel, artery or line in a river, railroad, highway, canal or other tributary system.

(15) In telephony, a telephone line or channel between two central offices or switching devices that is used in providing telephone connections between subscribers generally (also called a “tie-line”).

(16) In telegraphy, a telegraph line or channel between two main or central offices.

(17) In telecommunications, to provide simultaneous network access to multiple clients by sharing a set of circuits, carriers, channels or frequencies.

(18) In clothing, brief shorts (loose-fitting or tight) worn by men chiefly for boxing, swimming and athletics (some historically known as “trunk hose”.

(19) In zoology, the elongated prehensile, flexible, cylindrical nasal appendage of the elephant and certain other creatures (the proboscis).

(20) In nautical use, a large enclosed passage through the decks or bulkheads of a vessel, used as air ducting for purposes of heating, cooling, ventilation and such.

(21) In shipbuilding, any of various watertight casings in a vessel, as the vertical one above the slot for a centerboard in the bottom of a boat.

(22) A long tube through which pellets of clay, peas etc are driven by the force of the breath; a peashooter (archaic).

(23) In software engineering, the most current source tree, from which the latest unstable builds (so-called “trunk builds”) are compiled.

1400–1450: From the late Middle English tronke & trunke, from the Old French tronc (alms box, tree trunk, headless body), from the Latin truncus (stem, a stock, lopped tree trunk), a noun use of the adjective truncus (lopped; cut off, maimed, mutilated), (the later related to the English truncated).  Trunk & trunking are nouns & verbs, trunkful is a noun, trunked is a verb & adjective and trunkless is an adjective; the noun plural is trunks.

There are a myriad of “truck” terms in human pathology and other derived phrases include “elephant's trunk” (rhyming slang for “drunk”), “hand trunk” (a piece of luggage smaller than the traditional trunk and able to be carried by one), “junk in one's trunk” (corpulence of the buttocks, the alternative forms being “dump truck” or the vernacular “fat ass”), “the apple does not fall far from the trunk” (a variant of “the apple/pear etc does not fall far from the tree”) (children tend in appearance & characteristics to resemble their parents), “trunklid” (literally obviously “the lid of a trunk” and used of the opening panel which provides access to a car’s trunk), “bootlid” the UK equivalent and confusingly in the US used also as “decklid” on the basis of the trunk being a part of a car’s “rear deck”), “trunk novel” (a novel abandoned by the author while still a project), “trunk or treat” (an organized alternative to trick-or-treating where candy is handed out to children from cars in a parking lot; it was introduced as a child safety measure), “trunk show” (an event in which vendors present merchandise directly to store personnel or customers at a retail location or other venue, based on the idea of selling “out of a trunk”), “trunk sale” (and event at which goods are displayed for sale in the trunks of cars), “boot sale” the companion term)), “trunking” (travelling sitting in the trunk of a car”), and “trunk shot” (in film-making, a cinematic shot from within a car trunk (although there was a case of a serial killer who shot his victims while concealed in the trunk of a car.

Louis Vuitton Trunk #5 (left) and Louis Vuitton Trunk on Fire (right) by Tyler Shields (b 1982).

The original idea of a trunk being a “box; case etc” may lie in the first such “trunks” being hollowed-out tree trunks although some suggest the post-classical development of the meaning “box, case with a lid or top” was based on the notion of human body’s trunk being a “case” in which the organs were transported.  The modern idea of a “luggage compartment of a motor vehicle” dates from circa 1930, about the time trunks cease to be something separately carried and replaced by and space for luggage integrated into the bodywork.  The use of trunk had long been familiar in the medical literature (both of the torso and blood vessels etc) and the idea was by 1843 extended to railroad trunk lines and telephone networks by 1889.  “Trunk-hose” were first sold in the 1630s and seems to have been a kind of thermal underwear, the description a reference to them covering the whole torso (ie, the trunk) as opposed to most “hose” which was for the lower limbs.

The use of trunk to describe the “long snout of an elephant (or other beast with a similar appendage)” appeared first in the 1560s but etymologists are divided on whether it was an allusion to a tree’s trunk or has some connection with “trumpet”, based on the loud sound elephants are able to generate although the evidence does suggest the early use may have been a reference to the thing’s ability to hold water.  Predictably, by the early eighteenth century, it was a slang term for the human nose.  The use in clothing (always in the plural as “trunks”) emerged in the mid 1820s and initially described “short breeches of thin material”; it was a use of trunk in the sense of “torso”.  Use began in theatrical jargon but, as was not uncommon, soon it was applied to breeches generally, especially in US English and for the short, tight-fitting breeches worn by swimmers and other sporting types, adoption was close to universal by the 1890s.  “Swimming trunks” has survived as a regionalism; even within the one country, there are often several different names for what is one of humanity’s most simple garments.

Trump Trunks: MAGA (Make America Great Again) swimming trunks.  Trump trunks are made from a “silky, breathable, 4-way stretch mesh fabric” and features include (1) a small internal pocket, (2) a built-in anti-chafe liner.  The country of manufacture is not disclosed.  Clearly, the DNC (Democratic National Committee) in 2016 missed an opportunity by failing to release the "Crooked Hillary Clinton Bikini".

One linguistic curiosity was “subscriber trunk dialing” (later changed to “subscriber toll dialing” which later still switched to DDD (Direct Distance Dialing).  The “other” use of STD was as “sexually transmitted disease”, previously known as VD (venereal disease) and it wasn’t until the 1970s the initialism VD began to be replaced by STD (VD thought to have to have gained too many specific associations) but fortunately for the US telecommunications carrier American Telephone and Telegraph Company (later AT&T), in 1951 they renamed their STD service (for long-distance phone calls) to DDD, apparently for no better reason than the alliterative appeal although it's possible they just wanted to avoid mentioning “toll” with all the potential market resistance the word imparts.  Many countries in the English-speaking world continued to use STD for the phone calls, even after the public health specialists had re-purposed the initialization.  In clinical use, STI (Sexually Transmitted Infection)seems now the preferred term.

The evolution of the trunk: 1851 Concord stagecoach on display at the Smithsonian's National Postal Museum, Washington DC (left) with truck strapped to the back, additional trunks carried on the roof; 1928 Mercedes-Benz Nürburg 460 K Pullman Limousine (W08, centre left) with separate trunk still carried on a rear frame; 1936 Studebaker Dictator 4-door sedan (centre right) with the trunk now an integrated part of the bodywork and from that modest appendage they would grow.  The US full-sized cars of the 1960s & 1970s had most capacious trunks but few could match Leyland Australia's infamous P76 (1973-1975, right) which effortlessly could carry a 44 (imperial) gallon (53 US gallon; 205 litre) drum although the reputed ability to handle fours sets of golf clubs was probably more of a selling point.  Unfortunately, as the P76's rapid demise indicates, there just aren't that many golfers.

Drumming up business: Leyland P76 carrying 44 gallon drum in trunk.  Quite how many customers literally took advantage of this selling point isn't known but the large capacity was doubtless an attraction for some.

The compartment which is most located in the rear coachwork of an automobile is used for luggage and historically also the spare tyre a toolkit (neither now not always supplied).  In North American use, this is called a “trunk”, an inheritance from the time when the passengers’ trunks (ie, in the sense of the box-like suitcases) were strapped on to an extension at the back of horse-drawn carriages.  In the early automobiles, the practice continued (often with lined wicker baskets because they were of lightweight construction) and when these were integrated into the bodywork, the space provided continued to be called “the trunk”.  The British called the same thing a “boot”.  In horse-drawn carriages in the UK, a “boot” was a compartment used to store travel essentials, among which (in an age of rutted, poorly maintained roads) included boots, the male passengers sometimes required to push the coach when it became stuck in mud, the frequent inclusion of a “boot box” or “boot locker”, made typically of leather and attached at the rear.  The other suggested origin is the French boute (compartment; box).  The term “boot” thus spread throughout the British Empire although, under the Raj, in India & Ceylon (later Sri Lanka) it became the “dickie”.  That was based on the dicky seat (also as “dickie seat” & “dickey seat” and later more commonly known as the “rumble seat”), an upholstered bench mounted at the rear of a coach, carriage or early motorcar and as the car industry evolved and coachwork became more elaborate, increasingly they folded into the body.  The size varied but generally they were designed to accommodate one or two adults although the photographic evidence suggests they could be used also to seat half-a-dozen or more children.  Why it was called a dicky seat is unknown (the word dates from 1801 and most speculation is in some way related to the English class system) but when fitted on horse-drawn carriages it was always understood to mean “a boot (box or receptacle covered with leather at either end of a coach, the use based on the footwear) with a seat above it for servants”.  Under the Raj, “dickie” was preferred while the colloquial “mother-in-law seat” was at least trans-Atlantic and probably global.

Lindsay Lohan illustrates how there are frunks (left) and there are trunks (right).

The rear-engined Porsche 911 Carrera (997, 2004-2013) Cabriolet (Los Angeles, 2012, right) has a frunk while the front-engined Mercedes-Benz SL 65 AMG roadster (Los Angeles,  2005, right) has a trunk.  Based on the R230 (2001-2011) platform, the SL 65 AMG was produced between 2004-2012 and Ms Lohan also later drove an SL 550 (2006-2011), a model which was a quirk in the naming system because the designation was exclusive to the the North American market, the RoW (rest of the world) cars retaining the SL 500 badge even though both used the 5.5 litre (333 cubic inch) V8 (M273).  As the SL 65's open trunk lid reveals (right), because of the need to accommodate the bulky, folding aluminum hard-top, when lowered, it absorbed much of the trunk space so the design, like many, involved a trade-off between what was gained and what was lost.  Ms Lohan had (relatively) minor accidents in both her SL 65 and later a 911 coupé so clearly should avoid driving black, German cars.

The Fiat X1/9 (produced by Fiat 1972–1982 and Bertone from 1982–1989) featured both a frunk (left) and a trunk (right).

Most cars built have had the engine mounted in the front, thus most trunks appeared in the rear bodywork.  There have however been cars with engines behind the driver (such things were quite numerous until well into the 1970s) and these usually had a storage compartment at the front (where the engine otherwise would sit, under the hood (bonnet)).  Until the early years of the twentieth century, these seem just to have been called a “trunk” or “boot” but as electric vehicles began to appear in volume “frunk” (the construct being f(ront) + (t)runk) and the less popular “froot” (the construct being fr(ont) + (b)oot)) came into use.  There have been mid-engined cars which have both a trunk and a frunk and those in the diminutive Fiat X1/9 were surprisingly large while others (such as Ferrari's Dino 308 GT4 (1973-1980) & 208 GT4 (1975-1980), both badged as Ferraris after 1976) were of a less generous capacity, the frunk in the Dinos best suited to storing something the size of a topless bikini but the GT4 was a genuine four-seater (in the sense of a 2+2), something not often attempted with the mid-engined configuration.

When there was no trunk lid, luggage racks were a popular fitting: 1959 "bug-eye" (or "frog-eye" depending on location) Austin-Healey Sprite (left) and 1971 Chevrolet Corvette Convertible LS5 454/365 (right).

There have been cars (and not all of them were sports cars) with no trunk lid.  In the case of the Austin-Healey Sprite (1958-1971), the lack of the structure on the early versions (1958-1961) was a cost-saving measure (the same rationale that saw the planned retractable headlights replaced by the distinctive protuberances atop the hood (bonnet) which lent the cheerful little roadster its nickname (bug-eye in North American and frog-eye in the UK & most of the Commonwealth).  It had additional benefits including weight reduction and improved structural rigidity but the obvious drawback was inconvenience: to use the trunk one had to reach through the gap behind the seats.  It was easy to see why luggage racks proved a popular accessory, sales of which continued to be strong even when later versions of the Sprite (1961-1971) and the badge-engineered companion model (the MG Midget (1961-1980)) gained a trunk lid.

Have trunk, can travel: Nor Cal’s (of Stockton, California) trunk lid kit for Austin Healy Sprite, May 1961.  Note the standard-sized registration (license) plate; the Sprite really was small.

However, noting Austin-Healey’s cost-cutting meant the Series 1 Sprite’s trunk came lidless, modern commerce quickly saw a gap (technically also a “lack of gap”) in the market and “lid kits” soon appeared.  Advertised as meaning “no more acrobatic maneuvers when loading luggage”, mention was made also of an installation making the spare tyre easier to reach, a matter in the early 1960s of some significance because tyres then were not as durable and punctures more frequent.  The advertising copy was selective in that it mentioned “no welding necessary” but neglected to point out an owner would need to cut the required hole but presumably, that would have been obvious.  It was a proper trunk lid in that it was lockable and said also to be “waterproof”, the latter a quality owners of British sports cars really didn’t expect so that novelty would have been a selling point.  For those Sprite owners whose family had gained a child, the improved accessibility to the trunk would have been most helpful because, as parents know, going anywhere with an infant requires carrying a large bag of stuff.  They might also have been attracted to the "baby seat" available as an accessory from the Healey factory; it was a design which would now be thought extraordinary (other words also come to mind) but it was at the time just the way things were done.

1962 MG Midget.

When the updated Austin-Healey Sprite and the companion MG Midget were released in 1961, the re-design included a trunk-lid, making the little machines more practical although niceties like external door handles and side-windows were until 1964 thought unnecessary luxuries.  With the addition of a trunk lid, the rear wheel arches were given a “flattened top”, the explanation being the additional metal was required to ensure structural rigidity because the large hole cut to allow a lid meant there would be too much “lateral flex” were the old round arches retained.  It was thus a surprise when late in 1971 the round wheel arches re-appeared so either British Leyland used some body-engineering technique to achieve the required strength with less steel or it had been concluded the original conclusions were too conservative.  The change was welcomed because not only did it improve the look but it made it easier to fit wider wheels and tyres, something of great interest to the many using their Midgets in competition.

Desirable 1973 "RWA" MG Midget (left) and 1976 "Rubber Bumper" MG Midget (right); the rubber bumpers at the front looked even worse.  

The change however didn’t last; in 1974 the previously used wheel arches were back, the engineers at the time citing the need for additional body strength because US impact regulations had forced them to fit heavy (and ugly) rubber-fronted bumper bars.  That may have been true but the speculation has long been it was done also to disguise the way the body had been raised on its suspension, that unfortunate change made to ensure the low-slung roadster could comply with US minimum headlight height rules.  So, like the MGB, the Midget after 1974 was heavier, less powerful and slower than before, added to which the increased ride-height raised the centre of gravity so anti-roll bars had to be fitted to disguise the effect on the handling.  Despite that, both would remain in production until the end of the decade and demand was strong even when the ranges were terminated, the modest machines having much charm.  In the MG community, the Midgets with the round wheel arches are known as “RWAs” and they were never fitted to the last of the Sprites although at least one exists and it’s presumed that was a private conversion rather than something done by the factory.  

1963 Corvette (C2) Coupe. This was one of GM's official publicity stills and one can see why the decision was taken not to include a trunk lid but the absence enhanced structural integrity and it was this Chevrolet chose to emphasize.

Curiously, between 1953-1962, the Chevrolet Corvette (C1) did have a trunk lid but when the second generation (C2, 1962-1967) was released for the 1963 season, it had been removed and not until the fifth generation (C5) in 1998 did one again appear.  By then, the Corvette's luggage rack moment mostly had passed but into the twenty-first century they were still being fitted.  In the modern collector market, it’s one of those accessories, the very sight of which seems to upset some.

Trunks: The long and short of it.

1968 Holden HK Brougham (left) and 1970 Holden Premier (right).

The Holden Brougham (1968-1971) was not so much a landmark of the era as a cul-de-sac but it did indicate how quickly the “brougham” label had come to be associated with prestige and like Chevrolet’s Caprice, the Brougham was a response to a Ford.  In Australia, Ford had been locally assembling the full-sized Galaxies for the government and executive markets but tariffs and the maintenance of the Australian currency peg at US$1.12 meant profitability was marginal, so the engineers (with a budget said to be: "three-quarters of four-fifths of fuck all") took the modest, locally manufactured Falcon, stretched the wheelbase by five inches (125 mm), tweaked the front and rear styling (which although hardly radical resulted in a remarkably different look), added some gorp (the term bling not yet in use) and named it Fairlane.

The Fairlane name was chosen because of the success the company had had in selling first the full-sized US Fairlanes (nicknamed by locals as the “tank Fairlane”) between 1959-1962 and later the smaller version (1962-1965) which Robert McNamara (1916–2009 and briefly the president of Ford Motor Company before serving as US secretary of defense (1961-1968) under John Kennedy (JFK, 1917–1963; US president 1961-1963) & Lyndon Johnson (LBJ, 1908–1973; US president 1963-1969)) described as "the size of car Americans should be driving".  In that at least McNamara was right and what came in the 1960s to be called the "intermediates" (ie between the "compact" & "full-size" lines) proved a sweet spot in the market and that was because they were essentially the size of the "standard" US automobile before the breed became oversized in the mid-late 1950s.  The Australia Fairlane was for decades a successful and profitable product and eventually Holden (General Motors's (GM) local outpost) followed the formula but not before the curious diversion which was the Brougham.  For 1968, Holden chose what even at the time was thought a bizarre approach in trying to match the Fairlane; instead of a longer wheelbase (and thus more interior space), the Brougham was conjured up by extending the tail of the less exalted Premier by 8 inches (200 mm), the strange elongation a hurried and less than successful response.  Unwanted for decades when the could be bought for Aus$250, the handful of surviving Broughams became twenty-first century collectables, advertised for sale at as much as $Aus$90,000, some Holden connoisseurs (as one-eyed a crew as any) even finding a previously undetected elegance in the lines.

1958 Cadillac Series 62 Extended Length Sedan (Body Style 6239EDX, left) and 1958 Cadillac Series 62 Sedan (Body Style 6239, right).

In their defense, Holden could have pointed to a corporate precedent, the 1958 Cadillac range including the “Series 62 Extended Length Sedan”.  The Series 62 Sedan was already an impressive 216.8 inches (5.5 m) long but the Extended Length version measured an even more imposing 225.3 (5.7), the additional 8.5 inches (216 mm) all in the rear deck, creating a more capacious trunk.  There can’t have been many Cadillac buyers with that much luggage (although, impressionistically, golf club car parks did suggest there would be those for whom the ability to carry several sets of clubs might be compelling) but the new model did attract buyers, either despite or because of the healthy industry in jokes about Mafia functionaries and other figures in organized crime grateful finally to have more space to transport the bodies.  Unfortunately for Cadillac, there were only so many golfers and Mafia hit-men and despite 20,952 of the 103,455 (excluding Eldorados and “chassis only” sales) Series 62s produced in 1958 being the Extended Length Sedan (some 20%), it proved a single-season one-off which perhaps should have been a warning to Holden.

Cadillac's other take on the “long & slightly less long” of it: 1963 Cadillac Four-Window Sedan De Ville (Body Style 6239, left) and 1963 Cadillac Sedan De Ville Park Avenue (Body Style 6389, right).

Strangely, Cadillac’s next venture in rear-deck management went the other way, “short deck” versions of certain models offered between 1961-1963, the things created by removing 7 inches (178 mm) of aft bodywork, the effect more noticeable for the final season when the truncation was 8 inches (203 mm).  Demand, anyway muted, quickly declined and there ended Cadillac’s experiments with rear deck length.  There was at the time much criticism that “full-size” US cars had become too big but the “short deck” venture was most un-Cadillac like and, by international standards, the truck capacity of even the abbreviated models was still quite generous, able effortlessly to accommodate two sets of gold clubs, something which later became a de-facto standard in assessing the practicality of sports cars.  Jaguar used this feature as a selling point when the XK8 (1996-2006) was introduced because it wasn’t possible with all versions of the old E-Type (1961-1974).  For a variety of reasons, by the 1970s, there would be a smaller Cadillac and the first generation Seville (1975-1979) was most accomplished but of the even smaller Cimarron (1982–1988) there are few fond memories.  It wasn't that the Cimarron was, by the standards of its time, an especially bad car; it just wasn't "a Cadillac" as that construct was then understood.

1967 Ford GT40 Mark III (left) and 1967 Ford GT40 Mark I (road version, right).

From 1967 there was also a more contemporary example to inspire the antipodean engineers although it’s unlikely it much caught their eye; that was the Ford GT40 (1964-1969), one of the most successful machines in 1960s sports car racing which beat not only the competition but also the attempts by the Fédération Internationale de l'Automobile (the FIA; the International Automobile Federation) to legislate it into un-competitiveness,  Then (as now), the FIA was international sport’s dopiest regulatory body.  In the happy era when it was possible to make a few minor modifications and register a Le Mans race car for the road, 31 of the 105 GT40s were so configured (even a cigarette lighter was installed) but the driving experience was still very much that of a (slightly) quieter race car, the accommodation cramped, the ventilation marginal and the luggage space fit for little more than a proverbial topless bikini.  But some hardly souls bought them because there were few things on the road faster so thoughts turned to making a “more civilized” version with the creature comforts now expected.  Thus the 1967 GT40 Mark III with a slightly detuned engine, improved ventilation, a conventional, centrally mounted gear shift, sound deadening, more compliant suspension settings and even a reasonably sized ashtray to compliment the cigarette lighter.  However, only seven were built because they cost as much as a middle-class house, were still cramped (with challenging ingress and egress for all but the young or athletic) and in appearance differed in several aspects from the cheaper (Mark I) GT40 road cars still available from John Wyer (1909–1989).

Herbert von Karajan's 1967 Ford GT40 Mark III (Chassis M3/1105, left); of the seven produced, it was one of four LHD (left hand drive) versions and a GT40 Mark III "Luggage Box" (right).

By virtue of the long tail, the Mark III did though have more luggage space, the specially-fabricated "luggage box" behind the engine large enough to handle the luggage a couple would have packed for a dirty weekend while the frunk could have held little more than a conductor's baton though that may be unrelated to the Mark III's most famous owner being the Austrian conductor Herbert von Karajan (1908–1989).  The Mark III was fitted with additional sound deadening and the exhaust system made the sometimes Wagnerian sound of the 289 cubic inch (4.7 litre) V8 less intrusive but inside it was no Rolls-Royce and certainly not a 1965 Ford Galaxie (which Ford paid acoustic engineers to prove was quieter than a Rolls-Royce Silver Cloud III) so those who fitted the optional radio and cassette tape player would have had to turn the volume high.  Other options included tinted glass, air-conditioning and, remarkably, even a television.  It would anyway have been better to focus on the road because even in its detuned form the GT40 Mark III could be a handful, especially to those unacquainted with the then still novel characteristics of mid-engined road cars although Karajan also for a while drove a Mercedes-Benz 300 SL Gullwing (W198, 1954-1957) so he may have been not unfamiliar with quirky handling.  Wisely, he never drove his GT40 on wet roads.

1935 MG NA Magnette Allingham 2/4-Seater by Whittingham & Mitchel (left) and a burl walnut storage box mounted in the frunk (right).  The box was a custom fitting and most Magnettes were seen with the frunk simply carpeted.  Sometimes described by auction houses as a DHC (drophead coupé), this body style (despite what would come to be called 2+2 seating) really is a true roadster.  Note the six spare spark plugs in the engine bay; motoring used to be a much more maintenance-intensive business. 

The combination of a frunk and a front-mounted engine is unusual but it has been done.  What the coach-builder did with the MG Magnette was take advantage of what would otherwise be wasted space and the frunk typically was used as the place to store the car's tool-kit (sometimes an extensive inventory because such things often were needed, reliability then not what it became).  Frunks as a thing long pre-dated use of the term which seems to have come into use only in the 1990s (apparently part of the jargon among the cult of of rear-engined Porsche owners) but it was Tesla "formalizing" the terminology in the 2010s which made it mainstream.  The MG N-Type Magnette (1934-1936) used a 1271 cm³ (78 cubic inch) straight-six and while the combination of that many cylinders and a small displacement sounds curious, the configuration was something of an English tradition and a product of (1) a taxation system based on cylinder bore and (2) the attractive economies of scale and production line rationalization of “adding two cylinders” to existing four-cylinder units to achieve greater, smoother power with the additional benefit of retaining the same tax-rate.  Even after the taxation system was changed, some small-capacity sixes were developed as out-growths of fours.  Despite the additional length of the block, there remained between cowl (scuttle) and engine enough space to include a modest frunk.

1935 MG NA Magnette Allingham 2/4-Seater by Whittingham & Mitchel with dickie seat.  Note the resemblance of the front bucket seats to those used in the early (S1 3.8; 1961-1964) Jaguar E-Type (1961-1974).  While the scalloped shape was admired for its elegance they really weren't all that comfortable and there were few complaints when a pair with more prosaic lines was substituted.   

The other unusual feature included by Whittingham & Mitchel in this Magnette was a dickie ("rumble" to the Americans) seat as part of the cockpit.  Although most rumble seats were mounted in an aperture separated from the passenger compartment, in smaller vehicles the additional seat often was integrated but became usable (by people) only when the hinged cover was raised; otherwise, the rear-seat cushion was a nicely upholstered parcel shelf.  Stylistically, what this afforded the designers was the scope to make a car appear a rakish two-seat roadster but one with the practicality of seating four when the panel was folded back.  That's no longer done but the concept remains, some designers artfully now concealing rear-door handles to hint at the look of a two door coupé, something now made more plausible by the adoption of the "four-door coupé" motif for the few remaining sedans and (less successfully) many SUVs (sports utility vehicles).