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

The medical care facility scored well in terms of preventing urinary tract infections, reducing bed sores and limiting harmful events such as blood clots following a surgery, medical procedure or childbirth. —Sacbee.com, 24 Nov. 2025

According to a recent survey from the Idaho Commission for Libraries, an agency created by the Legislature, nearly all public libraries in the state comply with the 2024 harmful-materials law, State Librarian Stephanie Bailey-White told the Statesman. —Idaho Statesman, 24 Nov. 2025

Also note that many supplements also contain harmful and toxic substances that are not reported on the label. —Jennifer Lefton, Verywell Health, 24 Nov. 2025

But there’s also traffic, pesticides and other harmful chemicals and rats, cats and dogs to contend with. —Scottie Andrew, CNN Money, 23 Nov. 2025

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