Source : Webster's Revised Unabridged Dictionary (1913)

Conceivable \Con*ceiv"a*ble\, a. [Cf. F. concevable.]
   Capable of being conceived, imagined, or understood. ``Any
   conceivable weight.'' --Bp. Wilkins.

         It is not conceivable that it should be indeed that
         very person whose shape and voice it assumed.
                                                  --Atterbury.
   -- {Con*ceiv"a*ble*ness}, n. -- {Con*ceiv"a*bly}, adv.

Source : WordNet®

conceivableness
     n : the state of being conceivable [syn: {conceivability}]