Wordnet 3.0
ADJECTIVE (1)
1. 
 bearing or identified by an assumed (often pen) name; 
- Example: "the writings of Mark Twain are pseudonymous"
The Collaborative International Dictionary of English v.0.48:
Pseudonymous \Pseu*don"y*mous\, a. [Gr. ?; pseydh`s false + ?,
   ?, a name: cf. F. pseudonyme. See Pseudo-, and Name.]
   Bearing a false or fictitious name; as, a pseudonymous work.
   -- Pseu*don"y*mous*ly, adv. -- Pseu*don"y*mous*ness, n.
   [1913 Webster]
WordNet (r) 3.0 (2006):
pseudonymous
    adj 1: bearing or identified by an assumed (often pen) name;
           "the writings of Mark Twain are pseudonymous"