Source : Webster's Revised Unabridged Dictionary (1913)

Risible \Ris"i*ble\, a. [F., fr. L. risibilis, fr. ridere,
   risum, to laugh. Cf. {Ridiculous}.]
   1. Having the faculty or power of laughing; disposed to
      laugh.

            Laughing is our busines, . . . it has been made the
            definition of man that he is risible. --Dr. H. More.

   2. Exciting laughter; worthy to be laughed at; amusing.
      ``Risible absurdities.'' --Johnson.

            I hope you find nothing risible in my complaisance.
                                                  --Sir W.
                                                  Scott.

   3. Used in, or expressing, laughter; as, risible muscles.

   Note: Risible is sometimes used as a noun, in the plural, for
         the feeling of amusement and for the muscles and other
         organs used in laughing, collectively; as, unable to
         control one's risibles.

   Syn: Ludicrous; laughable; amusing; ridiculous -- {Risible},
        {Ludicrous}, {Ridiculous}.

   Usage: Risible differs from ludicrous as species from genus;
          ludicrous expressing that which is playful and
          sportive; risible, that which may excite laughter.
          Risible differs from ridiculous, as the latter implies
          something contemptuous, and risible does not.

Source : WordNet®

risible
     adj : arousing or provoking laughter; "an amusing film with a
           steady stream of pranks and pratfalls"; "an amusing
           fellow"; "a comic hat"; "a comical look of surprise";
           "funny stories that made everybody laugh"; "a very
           funny writer"; "it would have been laughable if it
           hadn't hurt so much"; "a mirthful experience"; "risible
           courtroom antics" [syn: {amusing}, {comic}, {comical},
           {funny}, {laughable}, {mirthful}]