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]