The Collaborative International Dictionary of English v.0.48:

Frolicsome \Frol"ic*some\, a.
   Full of gayety and mirth; given to pranks; sportive.
   [1913 Webster]

         Old England, who takes a frolicsome brain fever once
         every two or three years, for the benefit of her
         doctors.                                 --Sir W.
                                                  Scott.
   -- Frol"ic*some*ly, adv. -- Frol"ic*some*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

frolicsomeness
    n 1: lively high-spirited playfulness [syn: friskiness,
         frolicsomeness, sportiveness]