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

For animals with severe toxicities, dialysis can be used to treat kidney failure as well as to extract poisonous substances from the blood, preventing further damage. —The Washington Post, San Diego Union-Tribune, 14 Mar. 2026

If the flowers of sweet almond trees are pollinated with pollen from their bitter almond cousins, the resulting nuts are likely to be poisonous. —Joshua Siskin, Oc Register, 14 Mar. 2026

But for those who have grown weary of hearing the chants provide a poisonous soundtrack to matches, including Leeds United themselves, the time has come for change. —Simon Hughes, New York Times, 11 Mar. 2026

Some are edible, some are medicinal, some are poisonous, all are beautiful. —Carl R. Gold, Baltimore Sun, 7 Mar. 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