The Collaborative International Dictionary of English v.0.48:

Drinker \Drink"er\, n.
   One who drinks; as, the effects of tea on the drinker; also,
   one who drinks spirituous liquors to excess; a drunkard.
   [1913 Webster]

   Drinker moth (Zool.), a large British moth (Odonestis
      potatoria).
      [1913 Webster]

WordNet (r) 3.0 (2006):

drinker
    n 1: a person who drinks liquids
    2: a person who drinks alcoholic beverages (especially to
       excess) [syn: drinker, imbiber, toper, juicer] [ant:
       abstainer, abstinent, nondrinker]