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

The whisky was slightly poisonous. —Aj Willingham, AJC.com, 6 Apr. 2026

Marsha purchased the ingredients for this poisonous beverage at a local store. —Peter Van Sant, CBS News, 5 Apr. 2026

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

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