The Collaborative International Dictionary of English v.0.48:

Festivity \Fes*tiv"i*ty\, n.; pl. Festivities. [L. festivitas:
   cf. F. festivit['e].]
   1. The condition of being festive; social joy or exhilaration
      of spirits at an entertaintment; joyfulness; gayety.
      [1913 Webster]

            The unrestrained festivity of the rustic youth.
                                                  --Bp. Hurd.
      [1913 Webster]

   2. A festival; a festive celebration. --Sir T. Browne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

festivity
    n 1: any joyous diversion [syn: celebration, festivity]

Moby Thesaurus II by Grady Ward, 1.0:

168 Moby Thesaurus words for "festivity":
   Kaffeeklatsch, Mardi Gras, Saturnalia, amusement, anniversaries,
   assemblee, assembly, assignation, at home, ball, banquet, blowout,
   boisterousness, brawl, carnival, caucus, celebrating, celebration,
   celebrations, ceremony, cheer, cocktail party, coffee klatch,
   colloquium, commemoration, commission, committee, conclave,
   concourse, congregation, congress, conventicle, convention,
   conviviality, convocation, costume party, council, dance, date,
   diet, dinner, dinner party, do, donation party, dressing ship,
   eisteddfod, elation, entertainment, exultation, fair, fanfare,
   fanfaronade, feast, felicity, festival, festive occasion, fete,
   field day, fiesta, flourish of trumpets, forgathering, forum,
   frivolity, fun and games, gaiety, gala, gala affair, gala day,
   garden party, gathering, get-together, glee, good cheer,
   great doings, heartiness, hen party, high jinks, hilarity, holiday,
   holiday-making, hoopla, house party, house-raising, housewarming,
   jamboree, jollification, jollity, joviality, joyance, joyfulness,
   jubilance, jubilation, jubilee, kermis, larking, lawn party, levee,
   mad round, mafficking, marking the occasion, mask, masque,
   masquerade, masquerade party, meet, meeting, memorialization,
   memory, merriment, merrymaking, mirth, observance, ovation, panel,
   party, picnic, plenum, prom, quorum, racketing, rally,
   raucous happiness, reception, regale, regalement, rejoicing,
   religious rites, remembrance, rendezvous, revel, reveling,
   revelment, revelry, revels, rite, ritual observance,
   round of pleasures, salute, salvo, seance, session, shindig,
   shindy, show of joy, shower, sit-in, sitting, skylarking, smoker,
   soiree, solemn observance, solemnization, stag, stag party,
   surprise party, symposium, synod, testimonial, testimonial banquet,
   testimonial dinner, toast, treat, tribute, triumph, turnout,
   waygoose, wayzgoose, whoopee