poisonous

adjective

poi·​son·​ous ˈpȯiz-nəs How to pronounce poisonous (audio)
ˈpȯi-zᵊn-əs
Synonyms of poisonousnext
1
: destructive, harmful
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

Synonyms of poisonous

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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.
The incident comes a week after a horse died after ingesting a poisonous plant in the park. — Thomas Tracy, New York Daily News, 18 June 2026 Every part of the tree is poisonous, including the small round manchineel fruits, which are known to be fatal if ingested. — Steve Bender, Southern Living, 21 June 2026 The plant, which is non-native and is for ornamental purposes, is poisonous to horses. — Alexa Herrera, CBS News, 16 June 2026 The cane toad, also known as the bufo toad or the marine toad, is known for the large, poisonous glands behind its eyes that secrete toxins when it’s touched. — Amaia Gavica, Miami Herald, 23 June 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

poison oak
poisonous
poison out
See all Nearby Words

Cite this Entry

“Poisonous.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/poisonous. Accessed 7 Jul. 2026.

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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

Nglish: Translation of poisonous for Spanish Speakers

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