The Collaborative International Dictionary of English v.0.48:

Toxicology \Tox`i*col"o*gy\, n. [Gr. toxiko`n poison + -logy;
   cf. F. toxicologie. See Toxic. ]
   The science which treats of poisons, their effects,
   antidotes, and recognition; also, a discourse or treatise on
   the science.
   [1913 Webster]

WordNet (r) 3.0 (2006):

toxicology
    n 1: the branch of pharmacology that deals with the nature and
         effects and treatments of poisons