The Collaborative International Dictionary of English v.0.48:

Bacchanal \Bac"cha*nal\, a. [L. Bacchanalis. See Bacchanalia.]
   1. Relating to Bacchus or his festival.
      [1913 Webster]

   2. Engaged in drunken revels; drunken and riotous or noisy.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bacchanal \Bac"cha*nal\ (b[a^]k"k[.a]*nal), n.
   1. A devotee of Bacchus; one who indulges in drunken revels;
      one who is noisy and riotous when intoxicated; a carouser.
      "Tipsy bacchanals." --Shak.
      [1913 Webster]

   2. pl. The festival of Bacchus; the bacchanalia.
      [1913 Webster]

   3. Drunken revelry; an orgy.
      [1913 Webster]

   4. A song or a dance in honor of Bacchus.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bacchanal
    adj 1: used of riotously drunken merrymaking; "a night of
           bacchanalian revelry"; "carousing bands of drunken
           soldiers"; "orgiastic festivity" [syn: bacchanalian,
           bacchanal, bacchic, carousing, orgiastic]
    n 1: someone who engages in drinking bouts [syn: drunken
         reveler, drunken reveller, bacchanal, bacchant]
    2: a drunken reveller; a devotee of Bacchus [syn: bacchant,
       bacchanal]
    3: a wild gathering involving excessive drinking and promiscuity
       [syn: orgy, debauch, debauchery, saturnalia, riot,
       bacchanal, bacchanalia, drunken revelry]