Source : Webster's Revised Unabridged Dictionary (1913)

Incredulous \In*cred"u*lous\ (?; 135), a. [L. incredulus. See
   {In-} not, and {Credulous}.]
   1. Not credulous; indisposed to admit or accept that which is
      related as true, skeptical; unbelieving. --Bacon.

            A fantastical incredulous fool.       --Bp. Wilkins.

   2. Indicating, or caused by, disbelief or incredulity. ``An
      incredulous smile.'' --Longfellow.

   3. Incredible; not easy to be believed. [R.] --Shak.

Source : WordNet®

incredulous
     adj : not disposed or willing to believe; unbelieving [ant: {credulous}]