harmful

1 of 2

adjective

harm·​ful ˈhärm-fəl 

: of a kind likely to be damaging : injurious

harmful chemicals

harmfully

ˈhärm-fə-lē 

adverb

harmfulness noun

harmfulness

2 of 2

noun

harm·​ful·​ness

plural -es

: the quality or state of being harmful

Synonyms of harmful

Adjective

• detrimental
• damaging
• dangerous
• adverse
• bad

Examples of harmful in a Sentence

Adjective

DDT has been proven to be extremely harmful to the environment.

Recent Examples on the Web

Adjective

While Standard 100 focuses on harmful substances in the product, the organization’s Made in Green label also addresses production conditions and traceability. — Alexandra Harrell, Footwear News, 12 Oct. 2026

While ChatGPT isn’t a substitute for professional mental health care, our safeguards are designed to identify distress, safely handle harmful requests, and guide users to real-world help. — Laura Reiley, Vanity Fair, 9 Oct. 2026

That restriction extends the policy beyond individual conversations to services built around harmful interactions. — Aamir Khollam, Interesting Engineering, 8 Oct. 2026

Haugen expects better models to make fewer mistakes and catch more harmful content, but not all of it. — Beatrice Nolan, Fortune, 8 Oct. 2026

Word History

First Known Use

Adjective

14th century, in the meaning defined above

Rhymes for harmful

• armful

Kids Definition

harmful

adjective

harm·​ful ˈhärm-fəl 

: causing damage : injurious

harmfully

-fə-lē 

adverb

harmfulness noun

Legal Definition

harmful

adjective

harm·​ful

: of a kind likely to cause harm

harmfully adverb

harmfulness noun