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.
And again, a long-term question here, sort of about all the areas of American life that could be affected by AI, asking if these areas will be affected in a way that’s more good or more harmful. — NBC news, 6 Sep. 2026 And without one, treatment becomes guesswork, ineffective at best, harmful at worst. — Jerome Groopman, The New York Review of Books, 5 Sep. 2026 Around that time, the Department of Health and Human Services asked us to revise the CDC’s information for clinicians to include use of these unproven and potentially harmful treatments in children with measles. — Demetre Daskalakis, STAT, 4 Sep. 2026 Alzheimer’s disease is characterized by potentially harmful accumulations of two proteins. — Mike McRae 03, New Atlas, 3 Sep. 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 7 Sep. 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
Last Updated: - Updated example sentences
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