The Collaborative International Dictionary of English v.0.48:

Gabble \Gab"ble\, v. i. [imp. & p. p. Gabbled; p. pr. & vb. n.
   Gabbling.] [Freq. of gab. See Gab, v. i.]
   1. To talk fast, or to talk without meaning; to prate; to
      jabber. --Shak.
      [1913 Webster]

   2. To utter inarticulate sounds with rapidity; -- used of
      fowls as well as people; as, gabbling geese.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Gabble \Gab"ble\, n.
   1. Loud or rapid talk without meaning.
      [1913 Webster]

            Forthwith a hideous gabble rises loud
            Among the builders.                   --Milton.
      [1913 Webster]

   2. Inarticulate sounds rapidly uttered; as of fowls.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gabble
    n 1: rapid and indistinct speech [syn: jabber, jabbering,
         gabble]
    v 1: speak (about unimportant matters) rapidly and incessantly
         [syn: chatter, piffle, palaver, prate, tittle-
         tattle, twaddle, clack, maunder, prattle, blab,
         gibber, tattle, blabber, gabble]

Moby Thesaurus II by Grady Ward, 1.0:

163 Moby Thesaurus words for "gabble":
   absurdity, amphigory, babble, babblement, balderdash, bavardage,
   bibble-babble, blab, blabber, blah-blah, blather, blether,
   blethers, blubber, bombast, bull, bullshit, cackle, call, caquet,
   caqueterie, carol, caw, chat, chatter, cheep, chirk, chirp, chirr,
   chirrup, chitter, chitter-chatter, chuck, clack, claptrap, clatter,
   cluck, cock-a-doodle-doo, coo, croak, cronk, crow, cuckoo, dither,
   double-talk, drivel, drone, droning, drool, drum, fiddle-faddle,
   fiddledeedee, flummery, folderol, fudge, fustian, gab, gaggle,
   galimatias, gammon, gas, gibber, gibbering, gibberish,
   gibble-gabble, go on, gobble, gobbledygook, gossip, guff, guggle,
   gush, haver, hocus-pocus, honk, hoo, hoot, hot air, humbug,
   idle talk, jabber, jargon, jaw, jibber, maunder, maundering,
   mere talk, mouth, mouthing, mumble, mumbling, mumbo jumbo, murmur,
   murmuring, mutter, muttering, narrishkeit, natter, niaiserie,
   nonsense, nonsense talk, pack of nonsense, palaver, patter, peep,
   piffle, pip, pipe, pour forth, prate, prating, prattle,
   prittle-prattle, quack, ramble on, rant, rattle, rattle on,
   reel off, rigamarole, rigmarole, rodomontade, roll, rubbish,
   run on, scold, sing, skimble-skamble, sob, speak incoherently,
   splutter, spout, spout off, sputter, squawk, stuff and nonsense,
   stultiloquence, susurrate, susurration, talk away, talk nonsense,
   talk on, talkee-talkee, tittle-tattle, trash, trill, trumpery,
   twaddle, twattle, tweet, twiddle-twaddle, twit, twitter, vapor,
   vaporing, waffle, waffling, warble, whisper, whispering, whistle,
   yak, yakkety-yak