harmful

adjective

harm·​ful ˈhärm-fəl How to pronounce harmful (audio)
: of a kind likely to be damaging : injurious
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
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However, when intentions were ill-defined or assumed (sometimes based on hegemonic, often Christian, power dynamics), conversations about religious differences devolved from uncomfortable to hostile and even harmful. Matthew Mayhew, Forbes.com, 8 Sep. 2025 Along with the swamp eels, scientists in the USGS Wetland and Aquatic Research Center have been most concerned about the spread of Cuban tree frogs, which secrete noxious chemicals that are harmful to humans, and alligatorweed, which clogs waterways that can impact infrastructure. Wesley Bruer, CNN Money, 8 Sep. 2025 Anti-Inflammatory and Antioxidant Properties Whole turmeric contains antioxidant compounds that fight inflammation and neutralize harmful molecules known as free radicals. Lindsay Curtis, Verywell Health, 8 Sep. 2025 These perform well at low to medium heat, but begin to degrade around 500 °F, potentially releasing harmful fumes that can pose health risks. Katie Rosenhouse, Southern Living, 8 Sep. 2025 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 9 Sep. 2025.

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

More from Merriam-Webster on harmful

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