Source : Webster's Revised Unabridged Dictionary (1913)

Frivolous \Friv"o*lous\, a. [L. frivolus; prob. akin to friare
   to rub, crumble, E. friable: cf. F. frivole.]
   1. Of little weight or importance; not worth notice; slight;
      as, a frivolous argument. --Swift.

   2. Given to trifling; marked with unbecoming levity; silly;
      interested especially in trifling matters.

            His personal tastes were low and frivolous.
                                                  --Macaulay.

   Syn: Trifling; trivial; slight; petty; worthless. --
        {Friv"o*lous*ly}, adv. -- {Friv"o*lous*ness}, n.

Source : WordNet®

frivolousness
     n : the trait of being frivolous; not serious or sensible [syn:
         {frivolity}] [ant: {seriousness}]