The Collaborative International Dictionary of English v.0.48:

Cryptogram \Cryp"to*gram\ (kr?p"t?-gr?m), n.
   A cipher writing. Same as Cryptograph.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cryptogram
    n 1: a piece of writing in code or cipher [syn: cryptogram,
         cryptograph, secret writing]