harmful

adjective

harm·​ful ˈhärm-fəl 

: of a kind likely to be damaging : injurious

harmful chemicals

harmfully

ˈhärm-fə-lē 

adverb

harmfulness noun

Synonyms of harmful

• detrimental
• damaging
• dangerous
• adverse
• bad

Examples of harmful in a Sentence

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

Recent Examples on the Web

Part of that approach includes not waiting for proof before reducing potential harmful exposures. — Julia Vargas Jones, CNN Money, 20 Sep. 2026

To be sure, preserving room for joy can become harmful when treats interfere with other goals, produce debt, or leave behind regret and greater anxiety, Bryan-Podvin said. — Tatiana Sataua, Fortune, 20 Sep. 2026

But the term also alludes to deeply harmful and violent abuses against Black Americans throughout history. — Sofi Zeman, Kansas City Star, 17 Sep. 2026

The threat can become greater in the face of an adversarial prompt, in which an attacker attempts to cause a model to carry out a harmful action, such as revealing a password or other sensitive information. — Dan Goodin, ArsTechnica, 17 Sep. 2026

Word History

First Known Use

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