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

Air fresheners and strongly scented products also release volatile organic compounds and other harmful pollutants. — Dr. Lauren Zajac, Boston Herald, 19 July 2026

While the current fires continue to burn, the National Weather Service forecast shows the eastern United States can expect rain, which could help dampen harmful air for now. — Eduardo Cuevas, USA Today, 18 July 2026

Overall, explain early on why panic selling is harmful, as discussing this sooner saves both parties from crisis hand-holding later. — Expert Panel®, Forbes.com, 17 July 2026

Marylanders have been dealing with the harmful fumes this week in their daily jobs, with the air quality being harmful to sensitive groups. — The Baltimore Sun, Baltimore Sun, 17 July 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