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

But perhaps more alarmingly, Seneca Meadows is currently sending poisonous, PFAS-laden runoff into the Hudson and your drinking water supply. —Yvonne Taylor, New York Daily News, 21 Feb. 2025

Shauna, Van, and Akilah break free from the rest of the group and end up in a tunnel permeated by some sort of poisonous gas. —Esther Zuckerman, New York Times, 21 Feb. 2025

The warning comes by way of Fortinet, its latest report on the poisonous Snake Keylogger that has become one of the most persistent Microsoft Windows threats out in the wild. —Zak Doffman, Forbes, 19 Feb. 2025

Modern Australia is known for its array of wildlife: poisonous snakes and spiders, saltwater crocodiles, koalas, kangaroos, and more. —Laura Baisas, Popular Science, 19 Feb. 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