The Collaborative International Dictionary of English v.0.48:

Unoriginal \Unoriginal\
   See original.

WordNet (r) 3.0 (2006):

unoriginal
    adj 1: not original; not being or productive of something fresh
           and unusual; "the manuscript contained unoriginal
           emendations"; "his life had been unoriginal, conforming
           completely to the given pattern"- Gwethalyn Graham [ant:
           original]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "unoriginal":
   and, arid, back-number, banal, barren, bewhiskered, bromidic,
   common, commonplace, corny, cut-and-dried, derivative, dry, dull,
   earthbound, fade, familiar, fusty, hackney, hackneyed, infecund,
   infertile, literal, moth-eaten, mundane, musty, noncreative,
   nongerminal, nonseminal, old hat, platitudinous, prosaic, prosing,
   prosy, set, square, staid, stale, stereotyped, sterile, stock,
   stodgy, stolid, stuffy, threadbare, timeworn, trite, truistic,
   uncreative, unfanciful, unideal, unimaginative, uninspired,
   uninventive, unpoetic, unpregnant, unromantic, unromanticized,
   warmed-over, well-known, well-worn, worn, worn thin