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

Foxglove Foxglove features beautiful trumpet-like blossoms that are poisonous to cats. —Amy Deyoung, USA Today, 3 June 2026

Some have thorns or spines, others have poisonous leaves or berries, and still others have…elaborate chemical defense alarm systems? —Regina G. Barber, NPR, 3 June 2026

Chlorine gas is poisonous and classified as a pulmonary irritant that has a distinct odor. —Angel Saunders, PEOPLE, 3 June 2026

Ingesting poisonous mushrooms can lead to liver failure, kidney damage and neurological issues. —Sacbee.com, 1 June 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