pseudonym

from WordNet (r) 3.0 (2006)

pseudonym
    n 1: a fictitious name used when the person performs a
         particular social role [syn: {pseudonym}, {anonym}, {nom de
         guerre}]

from The Collaborative International Dictionary of English v.0.48

Pseudonym \Pseu"do*nym\, n. [Cf. F. pseudonyme. See
   {Pseudonymous}.]
   A fictitious name assumed for the time, as by an author; a
   pen name; an alias. [Written also {pseudonyme}.]
   [1913 Webster]