Source : Webster's Revised Unabridged Dictionary (1913)

Incredible \In*cred"i*ble\, a. [L. incredibilis: cf. OF.
   incredible. See {In-} not, and {Credible}.]
   Not credible; surpassing belief; too extraordinary and
   improbable to admit of belief; unlikely; marvelous; fabulous.

         Why should it be thought a thing incredible with you,
         that God should raise the dead?          --Acts xxvi.
                                                  8.

Source : WordNet®

incredible
     adj : beyond belief or understanding; "at incredible speed"; "the
           book's plot is simply incredible" [syn: {unbelievable}]
           [ant: {credible}]