Source : Webster's Revised Unabridged Dictionary (1913)

Antivenin \An`ti*ve"nin\, n. [Written also {antivenen},
   {antivenine}.] [Pref. anti- + L. venenum poison.] (Physiol.
   Chem.)
   The serum of blood rendered antitoxic to a venom by repeated
   injections of small doses of the venom.

Source : WordNet®

antivenin
     n : an antitoxin that counteracts the effects of venom from the
         bite of a snake or insect or other animal [syn: {antivenene}]