also gad-fly, 1620s, "fly which bites cattle," probably from gad (n.) "goad, metal rod," here in the sense of "stinger;" but the sense is entangled with gad (v.) "rove about" (on the notion, perhaps, of the insect's power of flight or of the restlessness of animals plagued by them), and another early meaning of gadfly was "someone who likes to go about, often stopping here and there" (1610s). Sense of "one who irritates another" is from 1640s (equivalent of Latin oestrus; see estrus). "In strictness, only the females are gadflies, the males being smaller and quite inoffensive, living on juices of plants" [Century Dictionary]. Earlier bot-fly, from bot "skin parasite" (late 15c.).

1886, gadjet (but said by OED corespondents to date from 1850s), sailors' slang word for any small mechanical thing or part of a ship for which they lacked, or forgot, a name; perhaps from French gâchette "catch-piece of a mechanism" (15c.), diminutive of gâche "staple of a lock." OED [2nd. ed. print, 1989] says derivation from gauge is "improbable."

1796, originally "Irish," now "pertaining to the Gaels" in the broadest sense; a "discriminated form" [Century Dictionary] of Gaelic.

metallic element, with element ending -ium + gadolinia, an earth named 1886 by J.C. Marginac in honor of Johan Gadolin (1760-1852), Finnish mineralogist and chemist, who in 1794 first began investigation of the earth (subsequently called gadolinite, 1802) which eventually yielded this element and several others.

1690s, a condensed form of some exclamation, usually said to be God's hooks (nails of Christ's Cross) or even God's hocks. Compare godsookers (1670s). The use of Gad for God (as in egad) is first attested 1590s. Among other similar "phraseological combinations" noted by OED (all from 17c.) were gadsbobs, gadslid, gadsniggers, gadsbudlikins, and gadsnouns; in all of which the second elements are sometimes said to be mere fanciful syllables.

see Gaia.

1810, from Scottish Gaelic Gaidheal "member of the Gaelic race" (Irish, Scottish, Manx), corresponding to Old Irish Goidhel (compare Latin Gallus under Gallic, also see Galatians). The native name in both Ireland and Scotland; owing to the influence of Scottish writers Gael was used in English at first exclusively of Highland Scots.

1774, "of or pertaining to the Gaels" (meaning originally in English the Scottish Highlanders); 1775 as a noun, "language of the Celts of the Scottish Highlands;" earlier Gathelik (1590s), from Gael (Scottish Gaidheal; see Gael) + -ic.

"blunder," 1909, perhaps from French gaffe "clumsy remark," originally "boat hook" (15c.), from Old Provençal gafar "to seize," probably from a Germanic source, from Proto-Germanic *gaf-, which is perhaps from PIE root *kap- "to grasp." Sense connection between the hook and the blunder is obscure; the gaff was used to land big fish. Or the Modern English word might derive from British slang verb gaff "to cheat, trick" (1893); or gaff "criticism" (1896), from Scottish dialect sense of "loud, rude talk" (see gaff (n.2)).

"cheap music hall or theater; place of amusement for the lowest classes," 1812, British slang, earlier "a fair" (1753), of unknown origin.