The Collaborative International Dictionary of English v.0.48:

Gibber \Gib"ber\ (j[i^]b"b[~e]r), n. [From Gib to balk.]
   A balky horse. --Youatt.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

gibber \gib"ber\ (g[i^]b"b[~e]r), v. i. [imp. & p. p. gibbered
   (g[i^]b"b[~e]rd); p. pr. & vb. n. gibbering.] [Akin to
   jabber, and gabble.]
   To speak rapidly and inarticulately. --Shak.

   Syn: jabber.
        [1913 Webster]

WordNet (r) 3.0 (2006):

gibber
    n 1: unintelligible talking [syn: gibberish, gibber]
    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]
    2: chatter inarticulately; of monkeys

Moby Thesaurus II by Grady Ward, 1.0:

144 Moby Thesaurus words for "gibber":
   absurdity, amphigory, babble, babblement, baffle, balderdash,
   bavardage, be Greek to, be beyond one, be too deep, beat one,
   bibble-babble, blab, blabber, blah-blah, blather, blether,
   blethers, blubber, bombast, bull, bullshit, cackle, caquet,
   caqueterie, chat, chatter, chitter-chatter, clack, claptrap,
   clatter, dither, double-talk, drivel, drone, droning, drool,
   escape one, fiddle-faddle, fiddledeedee, flummery, folderol, fudge,
   fustian, gab, gabble, galimatias, gammon, gas, gibbering,
   gibberish, gibble-gabble, go on, gobbledygook, gossip, guff, gush,
   haver, hocus-pocus, hot air, humbug, idle talk, jabber, jargon,
   jaw, jibber, lose one, maunder, maundering, mere talk, mouth,
   mouthing, mow, mumble, mumbling, mumbo jumbo, murmur, murmuring,
   mutter, muttering, narrishkeit, natter, need explanation,
   niaiserie, nonsense, nonsense talk, not make sense, not penetrate,
   pack of nonsense, palaver, pass comprehension, patter, perplex,
   piffle, pour forth, prate, prating, prattle, prittle-prattle,
   ramble on, rant, rattle, rattle on, reel off, riddle, rigamarole,
   rigmarole, rodomontade, rubbish, run on, skimble-skamble, sob,
   speak in tongues, speak incoherently, splutter, spout, spout off,
   sputter, stammer, stuff and nonsense, stultiloquence, stutter,
   susurrate, susurration, talk away, talk double Dutch,
   talk nonsense, talk on, talkee-talkee, tittle-tattle, trash,
   trumpery, twaddle, twattle, twiddle-twaddle, vapor, vaporing,
   waffle, waffling, whisper, whispering, yak, yakkety-yak, yammer