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

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

As Anna covers for Fyodor’s addiction and increasingly unstable professional behavior, her devotion starts to look poisonous for them both. — Alison Foreman, IndieWire, 5 Sep. 2026

But the point was just that Nick’s character is emulating Sheridan’s poisonous corrupted values, and the internet is a vehicle for that relationship. — Brian Davids, HollywoodReporter, 27 Aug. 2026

Eucalyptus oil and fresh leaves are poisonous when ingested or inhaled. — Sarah Bence, Verywell Health, 25 Aug. 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