The Collaborative International Dictionary of English v.0.48:

Carnival \Car"ni*val\, n. [It. carnevale, prob. for older
   carnelevale, prop., the putting away of meat; fr. L. caro,
   carnis, flesh + levare to take away, lift up, fr. levis
   light.]
   1. A festival celebrated with merriment and revelry in Roman
      Gatholic countries during the week before Lent, esp. at
      Rome and Naples, during a few days (three to ten) before
      Lent, ending with Shrove Tuesday.
      [1913 Webster]

            The carnival at Venice is everywhere talked of.
                                                  --Addison.
      [1913 Webster]

   2. Any merrymaking, feasting, or masquerading, especially
      when overstepping the bounds of decorum; a time of riotous
      excess. --Tennyson.
      [1913 Webster]

            He saw the lean dogs beneath the wall
            Hold o'er the dead their carnival     --Byron.
      [1913 Webster]

WordNet (r) 3.0 (2006):

carnival
    n 1: a festival marked by merrymaking and processions
    2: a frenetic disorganized (and often comic) disturbance
       suggestive of a large public entertainment; "it was so funny
       it was a circus"; "the whole occasion had a carnival
       atmosphere" [syn: circus, carnival]
    3: a traveling show; having sideshows and rides and games of
       skill etc. [syn: carnival, fair, funfair]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "Carnival":
   Advent, Allhallowmas, Allhallows, Allhallowtide, Annunciation,
   Annunciation Day, Ascension Day, Ash Wednesday, Candlemas,
   Candlemas Day, Christmas, Corpus Christi, Easter, Easter Monday,
   Easter Saturday, Easter Sunday, Eastertide, Ember days, Epiphany,
   Good Friday, Halloween, Hallowmas, Holy Thursday, Holy Week,
   Lady Day, Lammas, Lammas Day, Lammastide, Lent, Lententide,
   Mardi Gras, Martinmas, Maundy Thursday, Michaelmas, Michaelmas Day,
   Michaelmastide, Palm Sunday, Pancake Day, Passion Week, Pentecost,
   Quadragesima, Quadragesima Sunday, Septuagesima, Shrove Tuesday,
   Trinity Sunday, Twelfth-day, Twelfth-tide, Whit-Tuesday,
   White Sunday, Whitmonday, Whitsun, Whitsunday, Whitsuntide,
   Whitweek



Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "carnival":
   Broadway, Mardi Gras, Saturnalia, banquet, blowout, burlesque,
   burlesque show, circus, coochie show, do, drama,
   entertainment industry, fair, fantoccini, feast, festival,
   festive occasion, festivity, fete, field day, fiesta, floor show,
   gala, gala affair, gala day, galanty show, girly show,
   great doings, high jinks, hootchy-kootchy show, jamboree, kermis,
   leg show, legit, legitimate stage, light show, magic show,
   off Broadway, off-off-Broadway, ombres chinoises, party, peep show,
   picnic, playland, puppet show, raree-show, rep show,
   repertory drama, repertory show, rodeo, shadow show, show biz,
   show business, sideshow, stage world, stagedom, stageland, stock,
   strawhat, strawhat circuit, summer stock, the big top, the boards,
   the footlights, the scenes, the stage, the theater, theater world,
   theatromania, theatrophobia, variety, variety show, vaudeville,
   vaudeville show, waygoose, wayzgoose