The Collaborative International Dictionary of English v.0.48:

decode \decode\ v. t.
   to convert from a coded form into the original form; -- of
   communications. Inverse of encode.

   Syn: decrypt, decipher[WE1].
        [PJC]

WordNet (r) 3.0 (2006):

decode
    v 1: convert code into ordinary language [syn: decode,
         decrypt, decipher] [ant: encode]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "decode":
   anagram, answer, bottom, break, clear up, crack, cryptanalyze,
   debug, decipher, decrypt, disentangle, divine, do, dope, dope out,
   elucidate, explain, fathom, figure out, find out, find the answer,
   find the solution, get, get right, guess, guess right, have it,
   hit it, interpret, make out, open the lock, plumb, psych,
   psych out, puzzle out, ravel, ravel out, render, resolve, riddle,
   solve, sort out, translate, undo, unfold, unlock, unravel,
   unriddle, unscramble, untangle, untwist, unweave, work, work out



The Free On-line Dictionary of Computing (30 December 2018):

decode

    To apply decryption.

   (2004-05-22)