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

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

Wildfire smoke contains noxious or poisonous gases and particulate matter, tiny particles that can be inhaled deep into the lungs, affecting people with respiratory problems, says the Environmental Protection Agency. — Janet Loehrke, USA Today, 16 July 2026

How plants poisonous to dogs cause harm Not all toxic plants affect dogs the same way, but many share similar chemicals that attack the digestive system. — Ryan Brennan, Fort Worth Star-Telegram, 15 July 2026

Matters got worse after passersby with guns pinged holes in some of the barrels, and the poisonous stuff soaked about 15 feet down into the desert soil. — Patt Morrison, Los Angeles Times, 15 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