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

When Floyd is found dead at a community pool, surrounded by a poisonous cocktail and a vintage Playgirl magazine, two detectives (Richard Jenkins and Joy Sunday) begin unraveling the bizarre chain of events that led to his death. —Clayton Davis, Variety, 2 Apr. 2026

Although only a few species of poisonous mushrooms are fatal when ingested, many bear a resemblance to edible species. —Encyclopedia Britannica, 2 Apr. 2026

In 2007, Ardeshir Hosseinpour, a physicist in his mid-forties, was killed in Isfahan, either by radiation or by poisonous gas. —David D. Kirkpatrick, New Yorker, 30 Mar. 2026

Yes, hemlock plants are poisonous. —Markis Hill, Kansas City Star, 28 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