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

The active ingredient in them, Bifidobacterium longum, helps reduce harmful bacteria in your gut. — Bestreviews, Chicago Tribune, 14 Aug. 2026

France last month became the first country in the European Union to pass a blanket ban on the platforms amid rising worldwide concerns about the harmful effects of digital content on kids. — ABC News, 14 Aug. 2026

Key Takeaways Holding your pee for a short time is usually not harmful. — Amber J. Tresca, Verywell Health, 14 Aug. 2026

Fighting back The harmful content perpetrated online echoed concerns among consumers, leading them to find avenues to protect themselves. — Joshua Hong, Fortune, 14 Aug. 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