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]