toxicant

from WordNet (r) 3.0 (2006)

toxicant
    adj 1: having the qualities or effects of a poison [syn:
           {poisonous}, {toxicant}]
    n 1: any substance that causes injury or illness or death of a
         living organism [syn: {poison}, {toxicant}, {poisonous
         substance}]

from The Collaborative International Dictionary of English v.0.48

Toxicant \Tox"i*cant\, n.
   A poisonous agent or drug, as opium; an intoxicant.
   [1913 Webster]