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

• 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

Erin Patterson has been found guilty of murdering three relatives with poisonous mushrooms following a trial that has gripped the world. —Max Goldbart, Deadline, 7 July 2025

The atmosphere in the Rockies’ clubhouse is not toxic, unlike Chicago’s, which reportedly was poisonous for much of last season. —Patrick Saunders, Denver Post, 4 July 2025

All venomous snakes All poisonous amphibians Want these animals? —Craig Shoup, Nashville Tennessean, 3 June 2025

But the American people have been awakened to the poisonous influence the progressive left has and continues to have on American society. —Chris Roemer, Baltimore Sun, 8 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