Source : Webster's Revised Unabridged Dictionary (1913)

Inconvincible \In`con*vin"ci*ble\, a. [L. inconvincibilis. See
   {In-} not, and {Convince}.]
   Not convincible; incapable of being convinced.

         None are so inconvincible as your half-witted people.
                                                  --Gov. of the
                                                  Tongue.