The Collaborative International Dictionary of English v.0.48:

Stumble \Stum"ble\, v. t.
   1. To cause to stumble or trip.
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   2. Fig.: To mislead; to confound; to perplex; to cause to err
      or to fall.
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            False and dazzling fires to stumble men. --Milton.
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            One thing more stumbles me in the very foundation of
            this hypothesis.                      --Locke.
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The Collaborative International Dictionary of English v.0.48:

Stumble \Stum"ble\, v. i. [imp. & p. p. Stumbled; p. pr. & vb.
   n. Stumbling.] [OE. stumblen, stomblen; freq. of a word
   akin to E. stammer. See Stammer.]
   1. To trip in walking or in moving in any way with the legs;
      to strike the foot so as to fall, or to endanger a fall;
      to stagger because of a false step.
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            There stumble steeds strong and down go all.
                                                  --Chaucer.
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            The way of the wicked is as darkness: they know at
            what they stumble.                    --Prov. iv.
                                                  19.
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   2. To walk in an unsteady or clumsy manner.
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            He stumbled up the dark avenue.       --Sir W.
                                                  Scott.
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   3. To fall into a crime or an error; to err.
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            He that loveth his brother abideth in the light, and
            there is none occasion og stumbling in him. --1 John
                                                  ii. 10.
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   4. To strike or happen (upon a person or thing) without
      design; to fall or light by chance; -- with on, upon, or
      against.
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            Ovid stumbled, by some inadvertency, upon Livia in a
            bath.                                 --Dryden.
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            Forth as she waddled in the brake,
            A gray goose stumbled on a snake.     --C. Smart.
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The Collaborative International Dictionary of English v.0.48:

Stumble \Stum"ble\, n.
   1. A trip in walking or running.
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   2. A blunder; a failure; a fall from rectitude.
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            One stumble is enough to deface the character of an
            honorable life.                       --L'Estrange.
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WordNet (r) 3.0 (2006):

stumble
    n 1: an unsteady uneven gait [syn: lurch, stumble,
         stagger]
    2: an unintentional but embarrassing blunder; "he recited the
       whole poem without a single trip"; "he arranged his robes to
       avoid a trip-up later"; "confusion caused his unfortunate
       misstep" [syn: trip, trip-up, stumble, misstep]
    v 1: walk unsteadily; "The drunk man stumbled about" [syn:
         stumble, falter, bumble]
    2: miss a step and fall or nearly fall; "She stumbled over the
       tree root" [syn: stumble, trip]
    3: encounter by chance; "I stumbled across a long-lost cousin
       last night in a restaurant" [syn: stumble, hit]
    4: make an error; "She slipped up and revealed the name" [syn:
       stumble, slip up, trip up]

Moby Thesaurus II by Grady Ward, 1.0:

177 Moby Thesaurus words for "stumble":
   bad job, balk, barge, be all thumbs, bevue, blunder, blunder away,
   blunder into, blunder on, blunder upon, bobble, boggle,
   bonehead play, boner, boo-boo, botch, breakdown, bumble, bump,
   bump into, bungle, butcher, capsize, careen, career, chance, clump,
   clumsy performance, collapse, come a cropper, come across,
   come up against, comedown, commit a gaffe, crash, cropper, culbute,
   deflation, deviate, discover, dive, downfall, encounter, err,
   error, etourderie, fall, fall down, fall flat, fall headlong,
   fall into error, fall over, fall prostrate, fall upon, false move,
   false step, falter, faux pas, find, flop, flounce, flounder, flub,
   fluff, foozle, forced landing, fumble, gag, gaucherie,
   get a cropper, go amiss, go astray, go awry, go wrong, halt, hash,
   have two minds, haw, header, hem, hem and haw, hesitate, hit,
   hit upon, hum, hum and haw, inadvertence, inadvertency, jib, labor,
   lapse, lapsus calami, lapsus linguae, light, limp, list,
   loose thread, luck, lumber, lurch, mammer, mar, meet, mess,
   miscalculate, miscue, misstep, mistake, muck, muddle, muff, murder,
   nose dive, off day, omission, oversight, pause, pitch,
   pitch and plunge, play havoc with, plunge, pose, pratfall, reel,
   rock, roll, run across, sad work, scruple, seethe, shy, slip,
   slip up, slipup, smash, snapper, spill, spoil, sprawl,
   spread-eagle, stagger, stammer, stick, stickle, strain, stray,
   struggle, stump, stutter, sway, swing, tailspin, take a fall,
   take a flop, take a header, take a pratfall, take a spill,
   thrash about, tilt, topple, topple down, topple over, toss,
   toss and tumble, toss and turn, totter, trip, tumble, turn turtle,
   volutation, wallop, wallow, wander, waver, welter, wobble,
   wrong step