The Collaborative International Dictionary of English v.0.48:

Mistake \Mis*take"\, v. i.
   To err in knowledge, perception, opinion, or judgment; to
   commit an unintentional error.
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         Servants mistake, and sometimes occasion
         misunderstanding among friends.          --Swift.
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The Collaborative International Dictionary of English v.0.48:

Mistake \Mis*take"\ (m[i^]s*t[=a]k"), n.
   1. An apprehending wrongly; a misconception; a
      misunderstanding; a fault in opinion or judgment; an
      unintentional error of conduct.
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            Infallibility is an absolute security of the
            understanding from all possibility of mistake.
                                                  --Tillotson.
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   2. (Law) Misconception, error, which when non-negligent may
      be ground for rescinding a contract, or for refusing to
      perform it.
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   No mistake, surely; without fail; as, it will happen at the
      appointed time, and no mistake. [Low]
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   Syn: Blunder; error; bull. See Blunder.
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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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WordNet (r) 3.0 (2006):

mistake
    n 1: a wrong action attributable to bad judgment or ignorance or
         inattention; "he made a bad mistake"; "she was quick to
         point out my errors"; "I could understand his English in
         spite of his grammatical faults" [syn: mistake, error,
         fault]
    2: an understanding of something that is not correct; "he wasn't
       going to admit his mistake"; "make no mistake about his
       intentions"; "there must be some misunderstanding--I don't
       have a sister" [syn: mistake, misunderstanding,
       misapprehension]
    3: part of a statement that is not correct; "the book was full
       of errors" [syn: error, mistake]
    v 1: identify incorrectly; "Don't mistake her for her twin
         sister" [syn: mistake, misidentify]
    2: to make a mistake or be incorrect [syn: err, mistake,
       slip]