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

The lionfish's poisonous spikes can badly hurt anyone who’s stung. — ABC News, 30 July 2026

Ensure that chewable cords and poisonous plants are far out of reach. — Madeline Gunderson, USA Today, 29 July 2026

Authorities finally caught a break when the autopsy determined David’s likely cause of death was poisonous mushrooms found in his stomach. — Caroline Blair, PEOPLE, 25 July 2026

Lydia Kiesling’s Mobility attempts something at once more traditional and more ambitious, exploring how a young woman tries to disentangle herself from the oil industry’s poisonous tendrils. — Robert Rubsam, The Atlantic, 20 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