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):

frolicsome
    adj 1: given to merry frolicking; "frolicsome students
           celebrated their graduation with parties and practical
           jokes" [syn: coltish, frolicsome, frolicky,
           rollicking, sportive]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "frolicsome":
   animated, antic, capersome, coltish, exuberant, frisky,
   full of beans, gamesome, gay, hearty, impish, lively, merry,
   mischievous, playful, roguish, rollicking, rollicksome, rompish,
   skittish, spirited, sportful, sportive, sprightly, vital,
   vivacious, waggish, zestful, zippy