WordNet (r) 3.0 (2006):

inauthentic
    adj 1: intended to deceive; "a spurious work of art" [syn:
           inauthentic, unauthentic, spurious]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "inauthentic":
   absonant, contradictory, contrary to reason, fallacious, faulty,
   flawed, garbled, illogical, inconclusive, incongruous,
   inconsequent, inconsequential, inconsistent, invalid, irrational,
   loose, miscited, misquoted, misreported, misstated, nonscientific,
   not following, paralogical, reasonless, self-annulling,
   self-contradictory, self-refuting, senseless, spurious,
   unauthentic, unauthoritative, unconnected, unfounded,
   unphilosophical, unreasonable, unreliable, unscientific,
   without reason