The Collaborative International Dictionary of English v.0.48:

Prohibitionist \Pro`hi*bi"tion*ist\, n.
   [1913 Webster]
   1. One who favors prohibitory duties on foreign goods in
      commerce; a protectionist.
      [1913 Webster]

   2. One who favors the prohibition of the sale (or of the sale
      and manufacture) of alcoholic liquors as beverages.
      [1913 Webster]

WordNet (r) 3.0 (2006):

prohibitionist
    n 1: a reformer who opposes the use of intoxicating beverages
         [syn: dry, prohibitionist]