Word Origin & History
O.E. cocc, O.Fr. coq, O.N. kokkr, all of echoic origin. O.E. cocc was a nickname for "one who strutted like a cock," thus a common term in the Middle Ages for a pert boy, used of scullions, apprentices, servants, etc. A common personal name till c.1500, it was affixed to Christian names as a pet diminutive,
cf. Wilcox, Hitchcock, etc. Slang sense of "penis" is attested since 1618 (but cf. pillicock "penis," from c.1300); cock-teaser is from 1891. A cocker spaniel (1823) was trained to start woodcocks. Cock-and-bull is first recorded 1621, perhaps an allusion to Aesop's fables, with their incredible talking animals, or to a particular story, now forgotten. French has parallel expression coq-à-l'âne.
in various mechanical senses, such as cock of a faucet (late 15c.) is of uncertain connection with cock
(n.1), but Ger. has hahn "hen" in many of the same senses. The cock of an old matchlock firearm is 1560s, hence half-cocked "with the cock lifted to the first catch, at which
position the trigger does not act."
seeming contradictory senses of "to stand up" (as in cock one's ear), c.1600, and "to bend" (1898) are from the two cock nouns. The first is probably in reference to the posture of the bird's head or tail, the second to the firearm position. To cock ones hat carries the notion of "defiant boastfulness"
also in M.E. cocken (c.1150) "to fight."