The Collaborative International Dictionary of English v.0.48:

Bacchanalia \Bac`cha*na"li*a\ (b[a^]k`k[.a]*n[=a]"l[i^]*[.a]),
   n. pl. [L. Bacchanal a place devoted to Bacchus; in the pl.
   Bacchanalia a feast of Bacchus, fr. Bacchus the god of wine,
   Gr. Ba`kchos.]
   [1913 Webster]
   1. (Myth.) A feast or an orgy in honor of Bacchus.
      [1913 Webster]

   2. Hence: A drunken feast; drunken revels; an orgy.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Bacchanalia
    n 1: an orgiastic festival in ancient Greece in honor of
         Dionysus (= Bacchus) [syn: Dionysia, Bacchanalia]
    2: a wild gathering involving excessive drinking and promiscuity
       [syn: orgy, debauch, debauchery, saturnalia, riot,
       bacchanal, bacchanalia, drunken revelry]