The Collaborative International Dictionary of English v.0.48:

Blunder \Blun"der\, v. t.
   1. To cause to blunder. [Obs.] "To blunder an adversary."
      --Ditton.
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   2. To do or treat in a blundering manner; to confuse.
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            He blunders and confounds all these together.
                                                  --Stillingfleet.
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The Collaborative International Dictionary of English v.0.48:

Blunder \Blun"der\, n.
   1. Confusion; disturbance. [Obs.]
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   2. A gross error or mistake, resulting from carelessness,
      stupidity, or culpable ignorance.
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   Syn: Blunder, Error, Mistake, Bull.

   Usage: An error is a departure or deviation from that which
          is right or correct; as, an error of the press; an
          error of judgment. A mistake is the interchange or
          taking of one thing for another, through haste,
          inadvertence, etc.; as, a careless mistake. A blunder
          is a mistake or error of a gross kind. It supposes a
          person to flounder on in his course, from
          carelessness, ignorance, or stupidity. A bull is a
          verbal blunder containing a laughable incongruity of
          ideas.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Blunder \Blun"der\, v. i. [imp. & p. p. Blundered; p. pr. &
   vb. n. Blundering.] [OE. blunderen, blondren, to stir,
   confuse, blunder; perh. allied to blend to mix, to confound
   by mixture.]
   1. To make a gross error or mistake; as, to blunder in
      writing or preparing a medical prescription. --Swift.
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   2. To move in an awkward, clumsy manner; to flounder and
      stumble.
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            I was never distinguished for address, and have
            often even blundered in making my bow. --Goldsmith.
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            Yet knows not how to find the uncertain place,
            And blunders on, and staggers every pace. --Dryden.
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   To blunder on.
      (a) To continue blundering.
      (b) To find or reach as if by an accident involving more
          or less stupidity, -- applied to something desirable;
          as, to blunder on a useful discovery.
          [1913 Webster]

WordNet (r) 3.0 (2006):

blunder
    n 1: an embarrassing mistake [syn: blunder, blooper,
         bloomer, bungle, pratfall, foul-up, fuckup,
         flub, botch, boner, boo-boo]
    v 1: commit a faux pas or a fault or make a serious mistake; "I
         blundered during the job interview" [syn: drop the ball,
         sin, blunder, boob, goof]
    2: make one's way clumsily or blindly; "He fumbled towards the
       door" [syn: fumble, blunder]
    3: utter impulsively; "He blurted out the secret"; "He blundered
       his stupid ideas" [syn: blurt out, blurt, blunder out,
       blunder, ejaculate]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "blunder":
   absurdity, act of folly, bad job, be all thumbs, bevue, blooper,
   blow, blunder away, blunder into, blunder on, blunder upon, bobble,
   boggle, bollix, bonehead play, boner, boo-boo, botch, bull, bumble,
   bungle, butcher, careen, career, clumsy performance,
   commit a gaffe, dumb trick, err, error, etourderie, falter,
   faux pas, flounce, flounder, flub, fluff, folly, foozle, fumble,
   gaffe, gaucherie, goof, goof up, gum up, hash, howler, imprudence,
   indiscretion, labor, lapse, louse up, lumber, lurch,
   make a blunder, make a misstep, mar, mess, miscue, miss,
   miss the mark, misspeak, mistake, muddle, muff, murder, off day,
   pitch, pitch and plunge, play havoc with, plunge, reel, rock, roll,
   sad work, screw up, screw-up, seethe, slip, slip up, snapper,
   solecism, sottise, spoil, stagger, struggle, stumble, stupid thing,
   stupidity, sway, swing, thrash about, toss, toss and tumble,
   toss and turn, totter, trip, tumble, unwise step, wallop, wallow,
   welter