The Collaborative International Dictionary of English v.0.48:

Saturnalia \Sat`ur*na"li*a\, n. pl. [L. See Saturn.]
   1. (Rom. Antiq.) The festival of Saturn, celebrated in
      December, originally during one day, but afterward during
      seven days, as a period of unrestrained license and
      merriment for all classes, extending even to the slaves.
      [1913 Webster]

   2. Hence: A period or occasion of general license, in which
      the passions or vices have riotous indulgence.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Saturnalia
    n 1: an orgiastic festival in ancient Rome in honor of Saturn
    2: a wild gathering involving excessive drinking and promiscuity
       [syn: orgy, debauch, debauchery, saturnalia, riot,
       bacchanal, bacchanalia, drunken revelry]