Obelus

Obelus (pronounced ob-uh-luhs)

(1) A mark (− or ÷) used in ancient manuscripts to point out spurious, corrupt, doubtful, or superfluous words or passages.

(2) Another name for dagger (obsolete).

(3) As a dagger mark (†),used as a reference mark in printed matter, or (historically) to indicate that a person is deceased; now most often used to indicate a footnote.

(4) A mark (÷) used to represent division in mathematics.

1350–1400: A Middle English borrowing from the Late Latin from the Ancient Greek ὀβελός (obelós) (spit; pointed pillar).  The origin is something of a mystery, thought possibly an alteration of βέλος (bélos) but the initial vocal cannot be accounted for.  Etymologists agree the word is pre-Greek but there’s never been any evidence to suggest the source.  Obelus is a noun; the noun plural is obeli.

Said to be a creation of the Homeric scholar Zenodotus, the obelus was one of a system of editorial symbols used to enhance the meaning of documents.  The original use was twofold, a horizontal line indicating a critical mark to point out that a passage was spurious, but with one point below and one above (÷) (ὀβελὸς περιστιγμένος (obelòs peristigménos)) it denoted superfluous passages; these device were used especially in philosophical texts.  The original Zenodotuian set was expanded, firstly by Aristophanes of Byzantium (who invented the asterisk) and, in their most systematized form, by Aristarchus, thus the usually applied term Aristarchian symbols.  The dagger symbol, a later variant of the obelus, depicted an iron roasting spit, a dart, or the sharp end of a javelin, the symbolism suggesting a cutting-out of dubious material and remains common in modern typography.

Dagger obeli

In mathematics, the obelus is still used throughout the English-speaking world as the division sign, a use dating from an appearance in Teutsche Algebra (1659) by Swiss mathematician Johann Rahn.  That was accepted for centuries and endured even after the onset of modernity because the early mechanical adding-machines and electronic calculators included ÷ as the division key but, from the early-1980s, when IBM (more or less) standardized computer keyboards, a ÷ wasn’t included and software instead used the slash (/) for division.  Interestingly, although the asterisk (*) was used to perform the multiplication function, the necessary survival of the x on keyboards has meant the * has tended to be restricted to multiplication in software formulae and x is used in general text and equations.  The ISO 80000-2 standard for mathematical notation recommends only the slash (solidus or fraction bar) for division.  There is however a faction of mathematicians who have use neither for the ÷ or the -.  These purists insist there’s no such thing as division or subtraction, the operations respectively actually multiplication by fractions and the addition of negatives.