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

• envenomed
• poison
• poisoned
• 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 Palpatine's genius is less about those poisonous whispers than his plot to isolate Anakin from his friends. —Richard Edwards, Space.com, 24 Apr. 2025

The Big Bay Boom fireworks create a toxic fog of fine particles, poisonous aerosols and heavy metals that harm air, water and soil — posing serious risks to birds, wildlife, pets and people. —U T Readers, San Diego Union-Tribune, 22 Apr. 2025

TikTok, one particularly problematic Chinese export, is mental fentanyl designed to addict the Western masses and dupe them into poisonous ideologies—and Communist Party spyware, to boot. —David Faris, MSNBC Newsweek, 11 Apr. 2025

Historically, humans have used the poisonous fruit in a variety of ways: for murder, suicide, and even, in the case of the Madagascar witch trials of the 1800s, for proof of guilt or innocence. —Emily Kay Votruba, EverydayHealth.com, 8 Apr. 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