Origin and history of pair
pair(n.)
mid-13c., paire, "a set of two, two of a kind coupled in use," from Old French paire "pair, couple," and directly from Medieval Latin paria "equals," neuter plural of Latin par (genitive paris) "a pair, counterpart, equal," noun use of par (adj.) "equal, equal-sized, well-matched" (see par (n.)).
Originally of things. Of persons from late 14c., "a couple, a sexual pair." Used from late 14c. with a plural noun to denote a single tool or device composed essentially of two pieces or parts (shears, tongs, spectacles, etc.). Meaning "a woman's breasts" is attested from 1922. Pair bond (v.) is first attested 1940, in reference to birds mating.
pair(v.)
"to come together with another; be mated or married" (intransitive), also "to make a pair by matching" (transitive), c. 1600, from pair (n.). These senses now often are distinguished by pair off "separate from a company in pairs or couples" (1783) for the former and pair up (1863) for the latter. Related: Paired; pairing.
Entries linking to pair
1620s, "equality in value or circumstances," also "value of one currency in terms of another," from Latin par "equal, equal-sized, well-matched," also as a noun, "that which is equal, equality," a word of unknown and disputed origin. De Vaan is noncommittal. Watkins suggests perhaps from PIE root *pere- (2) "to grant, allot," with suggestion of reciprocality. Another guess connects it with PIE root *per- (5) "to traffic in, sell" (on notion of "give equal value for"). Meaning "a standard fixed by consent or by natural conditions, average or usual amount" is first attested 1767. Golf sense is attested by 1898, which led to the figurative use of par for the course for "fairly normal, what can be expected" (by 1928).