The Collaborative International Dictionary of English v.0.48:

Blather \Blath"er\ (bl[a^][th]"[~e]r), v. i. & t. [imp. & p. p.
   Blathered; p. pr. & vb. n. Blathering.] [Written also
   blether.] [Icel. bla[eth]ra. Cf. Blatherskite.]
   To talk foolishly, or nonsensically, or concerning matters of
   no consequence. --G. Eliot.

   Syn: babble, smatter, blether, blither.
        [Webster 1913 Suppl. + WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Blather \Blath"er\, n. [Written also blether.]
   Voluble, foolish, or nonsensical talk; -- often in the pl.
   --Hall Caine.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

blather
    n 1: foolish gibberish [syn: blather, blatherskite]
    v 1: to talk foolishly; "The two women babbled and crooned at
         the baby" [syn: babble, blather, smatter, blether,
         blither]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "blather":
   absurdity, amphigory, babble, babblement, balderdash, bavardage,
   be stupid, bibble-babble, blab, blabber, blah-blah, blatherskite,
   blether, blethers, blither, bombast, bosh, bull, bullshit, bunkum,
   burble, cackle, caquet, caqueterie, chat, chatter, chitter-chatter,
   clack, claptrap, clatter, dither, dote, double-talk, drivel, drool,
   fiddle-faddle, fiddledeedee, flapdoodle, flimflam, flummery,
   folderol, fudge, fustian, gab, gabble, galimatias, gammon, gas,
   gibber, gibberish, gibble-gabble, go on, gobbledygook, gossip,
   guff, gush, haver, hocus-pocus, hokum, hot air, humbug, idle talk,
   jabber, jargon, jaw, jazz, malarkey, maunder, mere talk,
   mumbo jumbo, narrishkeit, natter, niaiserie, nonsense,
   nonsense talk, pack of nonsense, palaver, patter, piffle,
   poppycock, pour forth, prate, prating, prattle, prittle-prattle,
   ramble on, rant, rattle, rattle on, reel off, rigamarole,
   rigmarole, rodomontade, rubbish, run on, skimble-skamble, slobber,
   spout, spout off, stuff and nonsense, stultiloquence, talk away,
   talk nonsense, talk on, talkee-talkee, tittle-tattle, trash,
   trumpery, twaddle, twattle, twiddle-twaddle, vapor, vaporing,
   waffle, waffling, yak, yakkety-yak