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

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

During the trial, prosecutors said investigators also found hemlock — a poisonous plant that can be fatal if ingested — in the family’s home, Courthouse News reported. — Nicole Acosta, PEOPLE, 10 July 2026

Cane toads, large and poisonous invasive amphibians, pose a threat to Floridian pets, particularly during the State's rainy season. — Sarah Perkel, USA Today, 8 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