poi·son (poi?z?n)n.1. A substance that causes injury, illness, or death, especially by chemical means.2. Something destructive or fatal.3. Chemistry A substance that inhibits another substance or a reaction: a catalyst poison.tr.v. poi·soned, poi·son·ing, poi·sons 1. To kill or harm with poison.2. To put poison on or into: poisoning arrows; poisoned the drink.3. a. To pollute: Noxious fumes poison the air. See Synonyms at contaminate.b. To have a harmful influence on; corrupt: Jealousy poisoned their friendship.4. Chemistry & Physics To inhibit (a substance or reaction).adj. Poisonous.[Middle English, from Old French, from Latin p?ti?, p?ti?n-, drink; see p?(i)- in Indo-European roots.]poi?son·er n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.poisoning (?p??z?n??) nthe act of killing someone using a poisonous substanceaccidental exposure to a toxic substanceCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014