poisonous

adjective

poi·​son·​ous ˈpȯiz-nəs 

ˈpȯi-zᵊn-əs

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

• poisoned
• poison
• toxic
• venomous

Examples of poisonous in a Sentence

Chocolate is poisonous to dogs.

This species of spider is extremely poisonous.

Recent Examples on the Web

The fourth, the Indian rhinoceros, is vulnerable, its habitat shrinking rapidly as fragmented and isolated population groups spread across a shattered landscape littered with invasive plant species poisonous to the animals. — Literary Hub, 22 Sep. 2026

Astronauts bring them on journeys to keep an eye on whether or not the water filtration systems are working, much the way miners used to take canaries down to the coal mines to check for poisonous gas leaks. — Leslie Felperin, HollywoodReporter, 18 Sep. 2026

All parts of poison hemlock are poisonous if ingested, and exposure can be fatal. — Sj McShane, Martha Stewart, 18 Sep. 2026

Spanish bluebells contain saponins, which smell and taste like soap, as well as poisonous cardiac glycosides. — ABC News, 8 Sep. 2026

Word History

First Known Use

15th century, in the meaning defined at sense 2

Kids Definition

poisonous

adjective

poi·​son·​ous ˈpȯiz-nəs 

-ᵊn-əs

: containing poison : having or causing an effect of poison

poisonously adverb

Medical Definition

poisonous

adjective

poi·​son·​ous ˈpȯiz-nəs, -ᵊn-əs 

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