Source : Webster's Revised Unabridged Dictionary (1913)

Frivolity \Fri*vol"i*ty\, n.; pl. {Frivolities}. [Cg. F.
   frivolit['e]. See {Frivolous}.]
   The condition or quality of being frivolous; also, acts or
   habits of trifling; unbecoming levity of disposition.

Source : WordNet®

frivolity
     n 1: the trait of being frivolous; not serious or sensible [syn:
          {frivolousness}] [ant: {seriousness}]
     2: something of little value or significance [syn: {bagatelle},
         {fluff}, {frippery}]
     3: acting like a clown or buffoon [syn: {buffoonery}, {clowning},
         {harlequinade}, {prank}]