harmful

adjective

harm·​ful ˈhärm-fəl How to pronounce harmful (audio)
Synonyms of harmfulnext
: of a kind likely to be damaging : injurious
harmful chemicals
harmfully adverb
harmfulness noun

Examples of harmful in a Sentence

DDT has been proven to be extremely harmful to the environment.
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
The same jury acquitted Lopez of more than a dozen other charges and hung on five counts of sending harmful material to a minor. Teri Figueroa, San Diego Union-Tribune, 31 Mar. 2026 While the video amused viewers, experts warn that repeatedly hitting the snooze button can be harmful. Lucy Notarantonio, MSNBC Newsweek, 31 Mar. 2026 Only a small fraction of fungi are harmful to humans, with the greatest risk to those with weakened immune systems. Brandi D. Addison, USA Today, 30 Mar. 2026 Those tensions were on display throughout the week, as lawmakers who appeared at the events acknowledged that the public is more concerned than ever about the potentially harmful impacts of AI. Bloomberg, Mercury News, 30 Mar. 2026 See All Example Sentences for harmful

Word History

First Known Use

14th century, in the meaning defined above

Time Traveler
The first known use of harmful was in the 14th century

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Cite this Entry

“Harmful.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/harmful. Accessed 3 Apr. 2026.

Kids Definition

harmful

adjective
harm·​ful ˈhärm-fəl How to pronounce harmful (audio)
: causing damage : injurious
harmfully adverb
harmfulness noun

Legal Definition

harmful

adjective
harm·​ful
: of a kind likely to cause harm
harmfully adverb
harmfulness noun

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