gab (v.) Look up gab at Dictionary.com
c.1200, "scoff, jeer; mock (someone), ridicule; reproach (oneself)," also "to lie to" (late 13c.), via Scottish and northern England dialect, from a Scandinavian source, such as Old Norse gabba "to mock," and probably in part from Old French gabber "mock, boast," which, too, is from Scandinavian; ultimately perhaps imitative. Meanings "speak foolishly; talk indiscreetly" are from late 14c. Meaning "to talk much" is from 1786, probably a shortening of gabble (v.). Related: Gabbed; gabbing. Gabber was Middle English for "liar, deceiver; mocker."
gab (n.) Look up gab at Dictionary.com
c.1200, "a gibe, a taunt;" mid-13c., "falsehood, deceit; idle talk," probably from a Scandinavian source akin to Old Norse gabb and in part from Old French gab, which also is probably from Scandinavian (compare gab (v.)). Gift of the gab "talent for speaking" is from 1680s.