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

Unsurprisingly, those who lose the most are at the greatest risk of harmful mental health outcomes. — Davis Giangiulio, CNBC, 4 Oct. 2026

Instinct says that information can still be used for AI training related to harmful content detection or safety research. — Kurt Knutsson, FOXNews.com, 3 Oct. 2026

Absorption methods have shown the ability to remove dissolved dyes without transforming them into potentially harmful off-products. — Jennifer Bringle, Footwear News, 2 Oct. 2026

More than 1,000 harmful substances have been found in e-waste or produced when it is improperly recycled, including lead, mercury, cadmium and other toxic chemicals, according to the World Health Organization. — Aniruddha Ghosal, Chicago Tribune, 1 Oct. 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