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.]
      [1913 Webster]

            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]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "decipher":
   account for, allegorize, analyze, answer, bottom, break,
   break down, cipher, clarify, clear up, crack, cryptanalyze, debug,
   decode, decrypt, demonstrate, demythologize, disentangle, divine,
   do, dope, dope out, elucidate, enlighten, euhemerize, exemplify,
   explain, explain away, explicate, exposit, expound, fathom,
   figure out, find out, find the answer, find the solution, get,
   get right, give reason for, give the meaning, guess, guess right,
   have it, hit it, illuminate, illustrate, interpret, make clear,
   make out, make plain, open the lock, paraphrase, plumb, popularize,
   psych, psych out, puzzle out, rationalize, ravel, ravel out, read,
   resolve, riddle, shed light upon, show, show how, show the way,
   simplify, solve, sort out, spell out, throw light upon, translate,
   undo, unfold, unlock, unravel, unriddle, unscramble, untangle,
   untwist, unweave, work, work out