allonym

from The Collaborative International Dictionary of English v.0.48

Allonym \Al"lo*nym\, n. [F. allonyme, fr. Gr. ? other + ? name.]
   1. The name of another person assumed by the author of a
      work.
      [1913 Webster]

   2. A work published under the name of some one other than the
      author.
      [1913 Webster]