The Collaborative International Dictionary of English v.0.48:

Jabber \Jab"ber\, v. i. [imp. & p. p. Jabbered; p. pr. & vb.
   n. Jabbering.] [Cf. Gibber, Gabble.]
   To talk rapidly, indistinctly, or unintelligibly; to utter
   gibberish or nonsense; to chatter. --Swift.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jabbering
    n 1: rapid and indistinct speech [syn: jabber, jabbering,
         gabble]