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

But major questions remained about how much space exists inside the Earth to store the CO2, how effectively it could be monitored and whether the poisonous, concentrated gas would reliably stay underground. — Katie Worth, ProPublica, 30 Oct. 2026

Mirroring the poisonous arena featured in the movie, Grace paired her vibrant, beaded Almée Couture gown with a high ponytail, leaving her blond bangs out to frame her face. — Arushi Jacob, Footwear News, 29 Oct. 2026

Now, a poisonous residue on the same crowbar has left him incapacitated. — Scott Tobias, Vulture, 21 Oct. 2026

This low-temperature, low-pressure hydrometallurgical method removes arsenic cleanly and operates without fossil fuels or poisonous gas emissions. — Mrigakshi Dixit, Interesting Engineering, 19 Oct. 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