gab (v.) Look up gab at
"to reproach," c.1200, via Scottish and northern England dialect, from a Scandinavian source, such as Old Norse gabba "to mock," or from Old French gabber "mock, boast," both perhaps ultimately imitative. Related: Gabbed; gabbing. Meaning "to talk much" is from 1786, probably a back-formation from gabble.
gab (n.) Look up gab at
early 14c., "mockery," from Old French gab, from gaber (see gab (v.)); meaning "idle talk" is by 1737. Gift of the gab "talent for speaking" is from 1680s.