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