The Collaborative International Dictionary of English v.0.48:

Blabber \Blab"ber\, n.
   one who blabr; a tattler; a telltale.

   Syn: blabbermouth. [1913 Webster]

WordNet (r) 3.0 (2006):

blabber
    n 1: one who reveals confidential information in return for
         money [syn: informer, betrayer, rat, squealer,
         blabber]
    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]