gab (v.) Look up gab at
"talk much," 1786, probably via Scottish and northern England dialect from earlier sense "speak foolishly; talk indiscreetly" (late 14c.), from gabben "to scoff, jeer; mock (someone), ridicule; reproach (oneself)," also "to lie to" (late 13c.), from a Scandinavian source, such as Old Norse gabba "to mock, make fun of," and probably in part from Old French gaber "to mock, jest; brag, boast," which, too, is from Scandinavian. Ultimately perhaps imitative (compare gabble, which might have shaded the sense of this word). Gabber was Middle English for "liar, deceiver; mocker." Related: Gabbed; gabbing.
gab (n.) Look up gab at
"action of talking," earlier "chatter, loquacity, idle talk" (mid-13c.), also "falsehood, deceit," originally "a gibe, a taunt" (c. 1200), mid-13c., probably from a Scandinavian source akin to Old Norse gabb "mocking, mockery," and in part from Old French gap, gab "joke, jest; bragging talk," which also is probably from Scandinavian (compare gab (v.)). Probably also there is influence from Scottish and northern English gab "the mouth" (see gob); OED reports the word "Not in dignified use." Gift of (the) gab "talent for speaking" is from 1680s.