The Collaborative International Dictionary of English v.0.48:

Decipher \De*ci"pher\, v. t. [imp. & p. p. Deciphered; p. pr.
   & vb. n. Deciphering.] [Pref. de- + cipher. Formed in
   imitation of F. d['e]chiffrer. See Cipher.]
   1. To translate from secret characters or ciphers into
      intelligible terms; as, to decipher a letter written in
      secret characters.
      [1913 Webster]

   2. To find out, so as to be able to make known the meaning
      of; to make out or read, as words badly written or partly
      obliterated; to detect; to reveal; to unfold.
      [1913 Webster]

   3. To stamp; to detect; to discover. [R.]
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            You are both deciphered, . . .
            For villains.                         --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decipher
    v 1: convert code into ordinary language [syn: decode,
         decrypt, decipher] [ant: encode]
    2: read with difficulty; "Can you decipher this letter?"; "The
       archeologist traced the hieroglyphs" [syn: decipher,
       trace]