Source : Webster's Revised Unabridged Dictionary (1913)

Risibility \Ris`i*bil"i*ty\, n. [CF. F. risibilit['e].]
   The quality of being risible; as, risibility is peculiar to
   the human species.

         A strong and obvious disposition to risibility. --Sir
                                                  W. Scott.

Source : WordNet®

risibility
     n : a disposition to laugh