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
ˈhärm-fə-lē How to pronounce harmful (audio)
adverb
harmfulness noun

Synonyms of harmful

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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.
But defining where harmless fun ends and harmful manipulation begins is far from straightforward. — Chloe Veltman, NPR, 25 Oct. 2026 That includes the 30x30 program to conserve 30% of California’s land and coastal waters by 2030, advanced protections for wetlands and new efforts to rein in the use of harmful pesticides and single-use plastic. — Los Angeles Times, 23 Oct. 2026 Of course, that doesn't mean every AI relationship is harmful. — Kurt Knutsson, FOXNews.com, 23 Oct. 2026 Without steering, the two larger models almost never chose a button described as harmful. — Shae Lake, Fortune, 22 Oct. 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

Rhymes for harmful

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Browse Nearby Words

harmer
harmful
harmfully
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Cite this Entry

“Harmful.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/harmful. Accessed 27 Oct. 2026.

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Kids Definition

harmful

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

Legal Definition

harmful

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