Merriam-Webster's Collegiate® Dictionary, 11th Edition
TOXIC
I. adjective
Etymology: Late Latin toxicus, from Latin toxicum poison, from Greek toxikon arrow poison, from neuter of toxikos of a bow, from toxon bow, arrow
Date: 1664
containing or being poisonous material especially when capable of causing death or serious debilitation , exhibiting symptoms of infection or toxicosis , extremely harsh, malicious, or harmful , toxicity noun
II. noun
Date: 1890
a toxic substance