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.
Ten coastal counties — from Humboldt to San Luis Obispo, outside of Mendocino and Marin — have seen hospitalizations due to poisonous wild mushroom ingestion, according to state public health data. Sean Campbell, Sacbee.com, 20 May 2026 More people have been sickened after eating poisonous mushrooms in Sacramento County, public health officials say. Cecilio Padilla, CBS News, 20 May 2026 At a time when our politics feel poisonous, public lands are an antidote. John Hickenlooper, Denver Post, 18 May 2026 The majority of people sickened by poisonous mushrooms in California since the outbreak began speak Spanish, though others speak Mandarin, Ukrainian, Russian, Mam and Mixteco (Indigenous languages in Central America). Evan Bush, NBC news, 15 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 24 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

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