A toxin (Greek: τοξικόν, toxikon)'s a poisonous substance produced by living cells or organisms. (Although technically man's a living organism, man-made substances created by artificial processes usually aren't considered toxins by this definition.) For a toxic substance not produced by living organisms, "toxicant"'s the more appropriate term, and "toxics"'s an acceptable plural. Toxins can be small molecules, peptides, or proteins that're capable of causing… (More on Toxin)