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

How poisonous is a black widow? —Tiffany Acosta, AZCentral.com, 6 Oct. 2025

Powell County paramedic Eddie Barnes and one of his team members were called to the Kentucky Reptile Zoo in May after the zoo’s co-director, James Harrison, was bitten by a poisonous mamba snake, local news outlet LEX 18 reported. —Toria Sheffield, PEOPLE, 27 Sep. 2025

Rather than allowing herself to be captured by the Romans, legend has it that Cleopatra let a poisonous asp bite her in Alexandria, according to the documentary. —Ashley Strickland, CNN Money, 26 Sep. 2025

Leninism, with its Bolshevik contempt for religion and family; Frantz Fanon's poisonous doctrine that violence is not only justified but the very path to human dignity; and Islamism's contempt for the West. —Ayaan Hirsi Ali, MSNBC Newsweek, 19 Sep. 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