The Collaborative International Dictionary of English v.0.48:

Stump \Stump\, v. t. [imp. & p. p. Stumped; p. pr. & vb. n.
   Stumping.]
   1. To cut off a part of; to reduce to a stump; to lop.
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            Around the stumped top soft moss did grow. --Dr. H.
                                                  More.
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   2. To strike, as the toes, against a stone or something
      fixed; to stub. [Colloq.]
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   3. To challenge; also, to nonplus. [Colloq.]
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   4. To travel over, delivering speeches for electioneering
      purposes; as, to stump a State, or a district. See To go
      on the stump, under Stump, n. [Colloq. U.S.]
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   5. (Cricket)
      (a) To put (a batsman) out of play by knocking off the
          bail, or knocking down the stumps of the wicket he is
          defending while he is off his allotted ground; --
          sometimes with out. --T. Hughes.
      (b) To bowl down the stumps of, as, of a wicket.
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                A herd of boys with clamor bowled,
                And stumped the wicket.           --Tennyson.
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   To stump it.
      (a) To go afoot; hence, to run away; to escape. [Slang]
          --Ld. Lytton.
      (b) To make electioneering speeches. [Colloq. U.S.]
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Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "stumped":
   addled, at a loss, at a nonplus, at a stand, at a standstill,
   at an impasse, baffled, bamboozled, beat, bewildered, buffaloed,
   confounded, dazed, floored, fuddled, in a dilemma, in suspense,
   licked, muddled, mystified, nonplussed, on tenterhooks, perplexed,
   puzzled, stuck, thrown