The Collaborative International Dictionary of English v.0.48:

Merriment \Mer"ri*ment\, n.
   Gayety, with laughter; mirth; frolic. "Follies and light
   merriment." --Spenser.
   [1913 Webster]

         Methought it was the sound
         Of riot and ill-managed merriment.       --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

merriment
    n 1: a gay feeling [syn: gaiety, merriment]
    2: activities that are enjoyable or amusing; "I do it for the
       fun of it"; "he is fun to have around" [syn: fun,
       merriment, playfulness]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "merriment":
   amusement, blithesomeness, buoyancy, celebration, cheer,
   cheerfulness, conviviality, elation, enjoyment, exhilaration,
   exuberance, exultation, felicity, festivity, flippancy, frivolity,
   fun, gaiety, glee, gleefulness, good cheer, good spirits,
   happiness, heartiness, high glee, high spirits, hilariousness,
   hilarity, holiday-making, hoopla, jocularity, jocundity,
   jollification, jolliness, jollity, joviality, joy, joyfulness,
   joyousness, jubilance, jubilation, jubilee, larking, laughter,
   levity, mafficking, merriness, merrymaking, mirth, mirthfulness,
   playfulness, prankishness, pranksomeness, racketing,
   raucous happiness, rejoicing, revel, reveling, revelment, revelry,
   revels, roguishness, show of joy, skylarking, sportiveness,
   trickery, trickiness, triumph, waggery, waggishness, whoopee