Gab
late Middle English: probably from an obsolete word with the same spelling meaning ‘mock, scoff, tell lies’.
wiktionary
From Middle English gabben, from Old English gabban(“to scoff, mock, delude, jest”) and Old Norse gabba(“to mock, make sport of”); both from Proto-Germanic *gabbōną(“to mock, jest”), from Proto-Indo-European *ghabh-(“to be split, be forked, gape”). Cognate with Scots gab(“to mock, prate”), North Frisian gabben(“to jest, sport”), Middle Dutch gabben(“to mock”), Middle Low German gabben(“to jest, have fun”).
etymonline
gab (v.)
"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.)
"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 (n.2)); OED reports the word "Not in dignified use." Gift of (the) gab "talent for speaking" is from 1680s.
