gab

Etymology 1

Inherited from Middle English gab, gabbe, from Old Norse gabb (“jest, mockery”) (whence also Old French gab, gap (“mockery, derision, scorn”)). Cognate with Icelandic gabb (“hoax”).

noun

1. Idle chatter.
2. The mouth or gob.
3. One of the open-forked ends of rods controlling reversing in early steam engines.
   Loose eccentric reversing gear gave way about 1836 to the early forms of gab motion. … In 1840 Stephenson evolved a motion in which the gabs were connected directly to the valve spindle. 1940 July, S. Richards, “Locomotive Valve gear Development”, in Railway Magazine, page 412

Etymology 2

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”).

verb

1. (intransitive, obsolete) To jest; to tell lies in jest; exaggerate; lie.
2. (intransitive) To talk or chatter a lot, usually on trivial subjects.
3. (transitive, obsolete) To speak or tell falsely.