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

They are also known to trick miners into quarrying worthless ore, following veins of what appears to be copper or silver, but when smelted, is found to be without value or, worse, poisonous. —Literary Hub, 27 Oct. 2025

In that way, Michelle is a camera-ready cover for whatever Auxolith is up to, which, as the movie goes along, teases out a poisonous history, including opioid manufacturing that affected Teddy’s mother (Alicia Silverstone). —Jake Coyle, Boston Herald, 24 Oct. 2025

The scorpion, who will sting with their poisonous venom when hurt, is extremely intuitive and highly aware of their surroundings. —Lisa Stardust, Refinery29, 21 Oct. 2025

Nothing was more freeing than finally realizing how poisonous these people are. —Christina Dugan Ramirez, FOXNews.com, 21 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