The Collaborative International Dictionary of English v.0.48:

Dipsomaniac \Dip`so*ma"ni*ac\, n.
   One who has an irrepressible desire for alcoholic drinks.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dipsomaniac
    n 1: a person who drinks alcohol to excess habitually [syn:
         alcoholic, alky, dipsomaniac, boozer, lush,
         soaker, souse]