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

poisonously adverb

Synonyms

• 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

If touched, the toad’s poisonous glands emit toxins that can be rapidly absorbed in your dog’s bloodstream and kill her quickly. —Lois K. Solomon, Sun Sentinel, 8 Aug. 2025

While every season is different depending on the location, some of the past challenges have included walking across a tightrope over a cliff, rescuing themselves from a sinking car and invading a crate filled with poisonous gases and chemicals. —Caroline Blair, People.com, 7 Aug. 2025

Radioactive waste from the former ComEd Nuclear Generating Station in Zion yards from the shoreline doesn’t need another poisonous lakefront companion with the potential to taint Lake Michigan. —Charles Selle, Chicago Tribune, 6 Aug. 2025

Rat poison often contains dye to identify it as poisonous, officials said, but the dye does not always show up in the animal’s tissue. —Don Sweeney, Sacbee.com, 4 Aug. 2025

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