any poison produced by an organism, characterized by antigenicity in certain animals and high molecular weight, and including the bacterial toxins that are the causative agents of tetanus, diphtheria, etc., and such plant and animal toxins as ricin and snake venom.

Origin of toxin

First recorded in 1885–90; tox(ic) + -in2
Can be confusedtoxic toxin

Synonyms for toxin

See poison. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for toxin

Contemporary Examples of toxin

Historical Examples of toxin

  • The determining test for a toxin is its action on a living cell.

    The Fundamentals of Bacteriology

    Charles Bradfield Morrey

  • Probably it was the toxin in the blood which poisoned the heart.

    Aaron's Rod

    D. H. Lawrence

  • Now I have said enough about the toxin and some little about the anti-toxin of the Mind.

    Nuggets of the New Thought

    William Walker Atkinson,

  • "This bottle contains a weak solution of the toxin of fatigue," persisted Kennedy.

    The Social Gangster

    Arthur B. Reeve

  • When this vital seat is poisoned by the toxin, death is instantaneous.

    More Hunting Wasps

    J. Henri Fabre

British Dictionary definitions for toxin



any of various poisonous substances produced by microorganisms that stimulate the production of neutralizing substances (antitoxins) in the bodySee also endotoxin, exotoxin
any other poisonous substance of plant or animal origin
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for toxin

"organic poison," especially one produced by bacteria in an animal body, 1886, from toxic + -in (2).

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for toxin




A poisonous substance, especially a protein, that is produced by living cells or organisms and is capable of causing disease when introduced into the body tissues but is often also capable of inducing neutralizing antibodies or antitoxins.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for toxin



A poisonous substance, especially one produced by a living organism. Toxins can be products or byproducts of ordinary metabolism, such as lactic acid, and they must be broken down or excreted before building up to dangerous levels. Toxins can facilitate survival, as with snake venom that kills or immobilizes prey, or cyanide produced by some plants as a defense against being eaten. Bacterial toxins can sometimes be neutralized with antitoxins. Compare antitoxin.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.