The Collaborative International Dictionary of English v.0.48:

Defeat \De*feat"\, v. t. [imp. & p. p. Defeated; p. pr. & vb.
   n. Defeating.] [From F. d['e]fait, OF. desfait, p. p. ofe
   d['e]faire, OF. desfaire, to undo; L. dis- + facere to do.
   See Feat, Fact, and cf. Disfashion.]
   1. To undo; to disfigure; to destroy. [Obs.]
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            His unkindness may defeat my life.    --Shak.
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   2. To render null and void, as a title; to frustrate, as
      hope; to deprive, as of an estate.
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            He finds himself naturally to dread a superior Being
            that can defeat all his designs, and disappoint all
            his hopes.                            --Tillotson.
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            The escheators . . . defeated the right heir of his
            succession.                           --Hallam.
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            In one instance he defeated his own purpose. --A. W.
                                                  Ward.
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   3. To overcome or vanquish, as an army; to check, disperse,
      or ruin by victory; to overthrow.
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   4. To resist with success; as, to defeat an assault.
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            Sharp reasons to defeat the law.      --Shak.

   Syn: To baffle; disappoint; frustrate.
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WordNet (r) 3.0 (2006):

defeated
    adj 1: beaten or overcome; not victorious; "the defeated enemy"
           [ant: undefeated]
    2: disappointingly unsuccessful; "disappointed expectations and
       thwarted ambitions"; "their foiled attempt to capture
       Calais"; "many frustrated poets end as pipe-smoking
       teachers"; "his best efforts were thwarted" [syn: defeated,
       disappointed, discomfited, foiled, frustrated,
       thwarted]
    n 1: people who are defeated; "the Romans had no pity for the
         defeated" [syn: defeated, discomfited]