Source : Webster's Revised Unabridged Dictionary (1913)

Hilarity \Hi*lar"i*ty\ (?; 277), n. [L. hilaritas: cf. F.
   hilarit['e]. See {Hilarious}.]
   Boisterous mirth; merriment; jollity. --Goldsmith.

   Note: Hilarity differs from joy: the latter, excited by good
         news or prosperity, is an affection of the mind; the
         former, produced by social pleasure, drinking, etc.,
         which rouse the animal spirits, is more demonstrative.

   Syn: Glee; cheerfulness; mirth; merriment; gayety;
        joyousness; exhilaration; joviality; jollity.

Source : WordNet®

hilarity
     n : great merriment [syn: {mirth}, {mirthfulness}, {glee}, {gleefulness}]