The Collaborative International Dictionary of English v.0.48:

Hater \Hat"er\ (h[=a]t"[~e]r), n.
   One who hates.
   [1913 Webster]

         An enemy to God, and a hater of all good. --Sir T.
                                                  Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hater
    n 1: a person who hates