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

poisonously adverb

Synonyms

• envenomed
• poison
• poisoned
• 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 attack, which only killed the bomber but could have been much worse, is an act worthy of perhaps the dumbest and most poisonous ideology on the planet right now. —Rich Lowry, National Review, 19 May 2025

From such small radioactive acorns do poisonous oaks grow. —Adam Gopnik, New Yorker, 19 May 2025

According to the McGill University office for science and society, several species of poison dart frogs contain such powerful toxins in their body that can kill an adult human by just brushing against its poisonous skin. —Maria Azzurra Volpe, MSNBC Newsweek, 14 May 2025

Residents near the area were later found to have usually high levels of the poisonous metal in their urine, according to the report. —Kiki Intarasuwan, CBS News, 14 May 2025

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