The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]

   Gift of gab, facility of expression. [Colloq.]
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "gift of gab":
   articulateness, big mouth, candor, command of language,
   command of words, communicativeness, conversableness,
   effective style, effusion, effusiveness, eloquence,
   eloquent tongue, expression, expressiveness, facundity,
   felicitousness, felicity, flow of words, flowing tongue, fluency,
   fluent tongue, flux de bouche, flux de paroles, flux of words,
   frankness, garrulity, garrulousness, gassiness, gift of expression,
   glibness, graphicness, gregariousness, gush, gushiness,
   long-windedness, loose tongue, loquaciousness, loquacity,
   meaningfulness, openness, oratory, prolixity, rhetoric,
   silver tongue, slickness, slush, smoothness, sociability,
   spate of words, talkativeness, verbosity, vividness, volubility,
   windiness