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

Over 100 landowners have denied power company surveyors access to their property, again demonstrating Maryland’s tenacity against harmful development which, frankly, no one asked for. — Adrianne Fantasia, Baltimore Sun, 9 Aug. 2026

Meta's critics say some of the most recognizable and potentially harmful aspects of Instagram and Facebook's designs are untouched by the ruling. — ABC News, 8 Aug. 2026

In the end, that realization helped Wood break his harmful cycle. — Tori Latham, Robb Report, 8 Aug. 2026

The group distributed them — along with test strips that identify other harmful adulterants, such as fentanyl, xylazine, and medetomidine — at clinics and neighborhood events. — Scott Maucione, NPR, 8 Aug. 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