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

Restoring the balance of the humors through profusely bleeding the patient or inducing vomiting or diarrhea with the poisonous plant hellebore. —Literary Hub, 28 Apr. 2026

There’s a steadiness to Tung/Wonder Woman that stands out for its quiet authority in a frequently goofy landscape peppered with poisonous robes and finger-eating minions. —Sarah Shachat, IndieWire, 24 Apr. 2026

The villain, though, is not Michael Jackson but his father, Joe, whose determination to get his boys out of Gary, Indiana, turns into something more poisonous. —Kelefa Sanneh, New Yorker, 20 Apr. 2026

Except for the Genetic Infantry, blue super soldiers engineered by the Southers to survive the poisonous atmosphere. —Jonathan M. Gitlin, ArsTechnica, 20 Apr. 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