poisonous

adjective

poi·​son·​ous ˈpȯiz-nəs How to pronounce poisonous (audio)
ˈpȯi-zᵊn-əs
Synonyms of poisonousnext
1
2
a
: having the properties or effects of poison
poisonous gas
b
: producing a toxic substance that causes injury or death when absorbed or ingested
poisonous mushrooms
also : venomous
a poisonous spider
3
: spiteful, malicious
poisonous rumors
poisonously adverb

Examples of poisonous in a Sentence

Chocolate is poisonous to dogs. This species of spider is extremely poisonous.
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
According to local media reports, Xu spent hundreds of thousands of yuan (tens of thousands of dollars) to buy highly toxic substances online, including alpha-amanitin, a lethal compound found in some poisonous mushrooms. CBS News, 27 May 2026 According to local media reports, Xu spent hundreds of thousands of yuan (tens of thousands of dollars) to buy highly toxic substances online, including alpha-amanitin, a lethal compound found in some poisonous mushrooms. ABC News, 26 May 2026 In the dark, predawn hours of December 3, 1984, a dense cloud of poisonous gas leaked from a pesticide plant and, borne on a soft, northern wind, enveloped Bhopal, a city in central India. Taran Dugal, New Yorker, 23 May 2026 In the Bay Area, poisonous mushrooms have been foraged in Alameda, Marin, Monterey, Napa, San Francisco, San Mateo and Sonoma counties, the health department said. Bay City News Service, Mercury News, 23 May 2026 See All Example Sentences for poisonous

Word History

First Known Use

15th century, in the meaning defined at sense 2

Time Traveler
The first known use of poisonous was in the 15th century

Browse Nearby Words

Cite this Entry

“Poisonous.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/poisonous. Accessed 29 May. 2026.

Kids Definition

poisonous

adjective
poi·​son·​ous ˈpȯiz-nəs How to pronounce poisonous (audio)
-ᵊn-əs
: containing poison : having or causing an effect of poison
poisonously adverb

Medical Definition

poisonous

adjective
poi·​son·​ous ˈpȯiz-nəs, -ᵊn-əs How to pronounce poisonous (audio)
1
: having the properties or effects of poison
poisonous gas
2
: producing a toxic substance that causes injury or death when absorbed or ingested
poisonous frogs and plants
also : venomous

More from Merriam-Webster on poisonous

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

More from Merriam-Webster