The Collaborative International Dictionary of English v.0.48:

Allopathy \Al*lop"a*thy\, n. [Gr. ? other + ? suffering, ?, ?,
   to suffer: cf. G. allopathie, F. allopathie. See Pathos.]
   That system of medical practice which aims to combat disease
   by the use of remedies which produce effects different from
   those produced by the special disease treated; -- a term
   invented by Hahnemann to designate the ordinary practice, as
   opposed to homeopathy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

allopathy
    n 1: the usual method of treating disease with remedies that
         produce effects differing from those produced by the
         disease itself [ant: homeopathy, homoeopathy]