Source : Webster's Revised Unabridged Dictionary (1913)

Gab \Gab\, n. [OE. gabbe gabble, mocking, fr. Icel. gabb
   mocking, mockery, or OF. gab, gabe; perh. akin to E. gape, or
   gob. Cf. {Gab}, v. i., {Gibber}.]
   The mouth; hence, idle prate; chatter; unmeaning talk;
   loquaciousness. [Colloq.]

   {Gift of gab}, facility of expression. [Colloq.]