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]

Moby Thesaurus II by Grady Ward, 1.0:

154 Moby Thesaurus words for "blabber":
   absurdity, amphigory, babble, babblement, balderdash, bavardage,
   be indiscreet, be unguarded, betray, betray a confidence, betrayer,
   bibble-babble, blab, blabberer, blabbermouth, blah-blah, blather,
   blether, blethers, blurt, blurt out, bombast, bull, bullshit,
   cackle, caquet, caqueterie, chat, chatter, chatterer,
   chitter-chatter, clack, claptrap, clatter, delator, dither,
   double-talk, drivel, drool, fiddle-faddle, fiddledeedee, fink,
   flummery, folderol, fudge, fustian, gab, gabber, gabble,
   galimatias, gammon, gas, gibber, gibberish, gibble-gabble,
   give away, go on, gobbledygook, gossip, guff, gush, haver,
   hocus-pocus, hot air, humbug, idle talk, inform, inform on,
   informer, jabber, jabberer, jargon, jaw, leak, let drop, let fall,
   let slip, magpie, mere talk, mumbo jumbo, narc, narrishkeit,
   natter, niaiserie, nonsense, nonsense talk, pack of nonsense,
   palaver, patter, peach, peacher, piffle, pour forth, prate, prater,
   prating, prattle, prattler, prittle-prattle, ramble on, rant, rat,
   rattle, rattle on, reel off, reveal a secret, rigamarole,
   rigmarole, rodomontade, rubbish, run on, sing, skimble-skamble,
   snitch, snitcher, spill, spill the beans, spout, spout off, spy,
   squeal, squealer, stool, stool pigeon, stoolie, stuff and nonsense,
   stultiloquence, talebearer, talk, talk away, talk nonsense,
   talk on, talkee-talkee, tattle, tattle on, tattler, tattletale,
   tell on, tell secrets, tell tales, telltale, tittle-tattle, trash,
   trumpery, twaddle, twattle, twiddle-twaddle, vapor, vaporing,
   waffle, waffling, whistle-blower, yak, yakkety-yak