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

The other problem is that many homes have more poisonous substances easily available than in the past, Willard said. —Madeline Holcombe, CNN Money, 9 Sep. 2025

Erin Patterson, who murdered three relatives with poisonous mushrooms, has been given a life prison sentence by the supreme court in Australia. —Max Goldbart, Deadline, 8 Sep. 2025

Wolf spider bites are not poisonous and won't cause sores or body-wide symptoms from its venom. —Carrie Madormo, Health, 6 Sep. 2025

This unconstitutional partisan politicization is poisonous to unit morale and discipline with long-term consequences for who serves and why. —Chicago Tribune, 5 Sep. 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