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

The editorial didn’t advise how to overcome tribal hatred and instead focused on the poisonous news of today — disruption and disorder in town halls and political vandalism of Tesla cars. —Chicago Tribune, 1 Apr. 2025

The machine fed the Southern identity a poisonous diet for three decades. —Peter Greene, Forbes.com, 1 Apr. 2025

Iago turns his sights to ruining Othello’s new wife, Desdemona (Molly Osborne), with false clues and poisonous innuendo. —Helen Shaw, New Yorker, 28 Mar. 2025

Work-from-home policies proved poisonous for downtowns, restaurants and the hospitality industry. —Debra J. Saunders, Orange County Register, 11 Mar. 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