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.
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   2. Erroneous; wrong; as, a mistaken notion.
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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]