Source : Webster's Revised Unabridged Dictionary (1913)

Ridiculous \Ri*dic"u*lous\, a. [L. ridiculosus, ridiculus, fr.
   ridere to laigh. Cf. {Risible}.]
   1. Fitted to excite ridicule; absurd and laughable; unworthy
      of serious consideration; as, a ridiculous dress or
      behavior.

            Agricola, discerning that those little targets and
            unwieldy glaives ill pointed would soon become
            ridiculous against the thrust and close, commanded
            three Batavian cohorts . . . to draw up and come to
            handy strokes.                        --Milton.

   2. Involving or expressing ridicule. [r.]

            [It] provokes me to ridiculous smiling. --Shak.

   Syn: Ludicrous; laughable; risible; droll; comical; absurd;
        preposterous. See {Ludicrous}. --- {Ri*dic"u*lous*ly},
        adv. -- {Ri*dic"u*lous*ness}, n.

Source : WordNet®

ridiculousness
     n : a message whose content is at variance with reason [syn: {absurdity},
          {absurdness}]