Source : Webster's Revised Unabridged Dictionary (1913)

Pseudonym \Pseu"do*nym\, n. [Cf. F. pseudonyme. See
   {Pseudonymous}.]
   A fictitious name assumed for the time, as by an author; a
   pen name. [Written also {pseudonyme}.]

Source : WordNet®

pseudonym
     n : a fictitious name used when the person performs a particular
         social role [syn: {anonym}, {nom de guerre}]