Fathom

Fathom (probounced fath-uhm)

(1) A unit of length equal to six feet (1.8288 m): used chiefly in nautical measurements and Admiralty papers.

(2) To measure the depth of by means of a sounding line; sound.

(3) In mining, a unit of volume usually equal to six cubic feet, used in measuring ore bodies (largely obsolete).

(4) In forestry, a unit of volume equal to six cubic feet, used for measuring timber (largely obsolete).

(5) To penetrate to the truth of; comprehend; understand.

Pre 900: From the Old English fæðm (length of the outstretched arm (a measure of about six feet), and figuratively, "power") from the Proto-Germanic fathmaz (embrace), related to the Old Norse faðmr (embrace) and the Old Saxon fathmos (the outstretched arms) and the Dutch vadem (a measure of six feet (1.8 m)).  The Middle English was fathme, cognate with the German Faden (a six-foot measure) and related to the Old English fæðmian (to embrace, surround, envelop), most forms at least influenced by the primitive Indo-European pot(ə)-mo-, a suffixed form of the root pete- (to spread).  Probable cognates included the Old Frisian fethem and the German faden (thread), the connection said to be the sense of "spreading out."  As a unit of measure, in an early gloss it appears for the Latin passus, which was about 5 feet (1.5 m).  The meaning "take soundings" is from circa 1600; its figurative sense of "get to the bottom of, understand" came some twenty years later.  The verb fathom was from the Old English fæðmian (to embrace, surround, envelop), from a Proto-Germanic verb derived from the source of the noun fathom, the cognates including the Old High German fademon and the Old Norse faþma.  The admiralty term fathomless (an adjective meaning literally "bottomless") is from the 1640s, later extended to figurative use (not to be comprehended).  Fathom is a noun and verb, fathomer & fathometer are nouns and fathomable, fathomless & (the predictably common) unfathomable are adjectives; the noun plural is fathoms.

The One-Hundred Fathom Line

UK Admiralty chart of the hundred fathom line, circa 1911.

The one-hundred fathom line is an Admiralty term for marking sea charts to delineate where the seabed lies at depths less or greater than 100 fathoms; it can thus be thought a particular expression of the continental shelf (though defined for military rather than geographical purposes).  Thus the distance from the coastlines of each land mass varies and it's related not at all to other boundaries established by the United Nation's (UN) Law of the Sea or other conventions such as territorial waters (historically 3 miles (5 km) and now 12 (20) or a state's Exclusive Economic Zone (EEZ) (200 (320)).  The hundred fathom line is now of little military significance (although it remains of interest to submariners) but it was cited as recently as 1952 in negotiations between the post-war Churchill (1951-1955) and Truman administrations (1945-1953) in defining the areas of preponderant operations for the Royal Navy and US Navy.

Lindsay Lohan GIF from A Beautiful Life (music video).  Although often photographed in the water, there's no evidence to suggest Ms Lohan has ever descended deeper than a a couple of fathoms.