Origin and history of half-wit

Old English half, halb (Mercian), healf (W. Saxon) "side, part," not necessarily of equal division (original sense preserved in behalf), from Proto-Germanic *halba- "something divided" (source also of Old Saxon halba, Old Norse halfr, Old Frisian, Middle Dutch half, German halb, Gothic halbs "half"), a word of no certain etymology. Perhaps from PIE root *skel- (1) "to cut," or perhaps a substratum word. Noun, adjective, and adverb all were in Old English.

Used also in Old English phrases, as in modern German, to mean "one half unit less than," for example þridda healf "two and a half," literally "half third." The construction in two and a half, etc., is first recorded c. 1200. Of time, in half past ten, etc., first attested 1750; in Scottish, the half often is prefixed to the following hour (as in German, halb elf = "ten thirty").

To go off half-cocked in the figurative sense "speak or act too hastily" (1833) is in allusion to firearms going off prematurely; half-cocked in a literal sense "with the cock lifted to the first catch, at which position the trigger does not act" is recorded by 1750. In 1770 it was noted as a synonym for "drunk." Bartlett ("Dictionary of Americanisms," 1848) writes that it was "a metaphorical expression borrowed from the language of sportsmen, and is applied to a person who attempts a thing in a hurry without due preparation, and consequently fails."

"mental capacity, the mind as the seat of thinking and reasoning," Old English wit, witt, more commonly gewit "understanding, intellect, sense; knowledge, consciousness, conscience," from Proto-Germanic *wit-, which is reconstructed to be from PIE root *weid- "to see," metaphorically "to know" (also compare wit (v.) and wise (adj.)).

The meaning "ability to connect ideas and express them in an amusing way" is recorded by 1540s, hence "quickness of intellect in speech or writing" (for nuances of usage, see humor (n.)). The sense of "person of wit or learning" is attested from late 15c.

To be at one's wit's end "perplexed, at a loss" is from late 14c. Witjar was old slang (18c.) for "head, skull." Witling (1690s) was "a pretender to wit." Witword was "testament." Also in Middle English of the sensitive faculty generally, and sensory impressions, as wittes five for the five bodily senses (c. 1200).

Germanic cognates include Old Saxon wit, Old Norse vit, Danish vid, Swedish vett, Old Frisian wit, Old High German wizzi "knowledge, understanding, intelligence, mind," German Witz "wit, witticism, joke," Gothic unwiti "ignorance."

A witty saying proves nothing. [Voltaire, Diner du Comte de Boulainvilliers]

Wit ought to be five or six degrees above the ideas that form the intelligence of an audience. [Stendhal, "Life of Henry Brulard"]