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

Though gorgeous with color, azaleas are poisonous to animals and humans when ingested. —Ashlyn Needham, Southern Living, 8 Apr. 2025

Every part of the pong pong tree is poisonous, but the leaves and barks aren’t as potent as the seeds. —Angela Haupt, Time, 7 Apr. 2025

Theo is afraid of this fiery phenomenon, writing to a spiritual mentor to ask if the comet’s tail is poisonous to humans and what scripture says about it. —Mary Ann Grossmann, Twin Cities, 6 Apr. 2025

Though gorgeous with color, azaleas are poisonous to animals and humans when ingested. —Ashlyn Needham, Southern Living, 8 Apr. 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