E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Gab (g hard).
The gift of the gab. Fluency of speech; or, rather, the gift of boasting. (French, gaber, to gasconade; Danish and Scotch, gab, the mouth; Gaelic, gob; Irish, cab; whence our gap and gape, gabble and gobble. The gable of a house is its beak.)
There was a good man named Job
Who lived in the land of Uz,
He had a good gift of the gob,
The same thing happened us,
Book of Job, by Zach. Boyd.
Thou art one of the knights of France, who hold it for glee and pastime to gab, as they term it, of exploits that are beyond human power.Sir W. Scott: The Talisman, chap. ii.