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

Cane toads, large and poisonous invasive amphibians, pose a threat to Floridian pets, particularly during the State's rainy season. — Sarah Perkel, USA Today, 8 July 2026

Shrouded completely in a thick, poisonous cloud cover, its surface is obviously impossible to observe. — Mike Lynch, Twin Cities, 5 July 2026

All of this played out against an increasingly poisonous political environment. — Eric Berger, ArsTechnica, 3 July 2026

Sago palm, oleander, foxglove, azaleas and lily of the valley are all common and all poisonous. — Ryan Brennan, Miami Herald, 2 July 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