The Collaborative International Dictionary of English v.0.48:

Mistake \Mis*take"\ (m[i^]s*t[=a]k"), v. t. [imp. & obs. p. p.
   Mistook (m[i^]s*t[oo^]k"); p. p. Mistaken
   (m[i^]s*t[=a]k"'n); p. pr. & vb. n. Mistaking.] [Pref. mis-
   + take: cf. Icel. mistaka.]
   1. To take or choose wrongly. [Obs. or R.] --Shak.
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   2. To take in a wrong sense; to misunderstand misapprehend,
      or misconceive; as, to mistake a remark; to mistake one's
      meaning. --Locke.
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            My father's purposes have been mistook. --Shak.
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   3. To substitute in thought or perception; as, to mistake one
      person for another.
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            A man may mistake the love of virtue for the
            practice of it.                       --Johnson.
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   4. To have a wrong idea of in respect of character,
      qualities, etc.; to misjudge.
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            Mistake me not so much,
            To think my poverty is treacherous.   --Shak.
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The Collaborative International Dictionary of English v.0.48:

Mistaken \Mis*tak"en\, p.a.
   1. Being in error; judging wrongly; having a wrong opinion or
      a misconception; as, a mistaken man; he is mistaken.
      [1913 Webster]

   2. Erroneous; wrong; as, a mistaken notion.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mistaken
    adj 1: wrong in e.g. opinion or judgment; "well-meaning but
           misguided teachers"; "a mistaken belief"; "mistaken
           identity" [syn: misguided, mistaken]
    2: arising from error; "a false assumption"; "a mistaken view of
       the situation" [syn: false, mistaken]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "mistaken":
   all wet, all wrong, amiss, catachrestic, distorted, eisegetical,
   erring, erroneous, fallacious, false, faulty, flawed, garbled,
   in error, inaccurate, incorrect, misapprehended, misconceived,
   misconstrued, misguided, misinformed, misinterpreted, misread,
   misunderstood, off, out of order, perverted, twisted,
   under an error, warped, wrong