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

The result has been a series of poisonous IMF prescriptions. —Jason Ma, Fortune, 13 Oct. 2025

Mothballs are poisonous and represent a significant danger to the family dog, especially those that tend to eat first and ask questions later. —Paul Cappiello, Louisville Courier Journal, 10 Oct. 2025

Horse chestnuts are poisonous and not edible. —Jenna Prestininzi, Freep.com, 9 Oct. 2025

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