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 cane toad, also known as the bufo toad or the marine toad, is known for the large, poisonous glands behind its eyes that secrete toxins when it’s touched. — Amaia Gavica, Miami Herald, 23 June 2026

Berlin — Authorities across Germany have been battling an aggressive outbreak of poisonous caterpillars, which can cause severe health issues and have led to the closure of parks and other outdoor spaces, including in Berlin. — Sophie Tanno, CNN Money, 23 June 2026

Every part of the tree is poisonous, including the small round manchineel fruits, which are known to be fatal if ingested. — Steve Bender, Southern Living, 21 June 2026

Just last week, a 16-year-old carriage horse in Central Park named Deniz died after ingesting a poisonous plant. — Nicole Acevedo, NBC news, 19 June 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