harmful

adjective

harm·​ful ˈhärm-fəl How to pronounce harmful (audio)
: 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.
In a lab study, fiber extracted from sweet potato skin increased beneficial bacteria and decreased harmful bacteria in the gut. Brittany Lubeck, Verywell Health, 10 Nov. 2025 Letting a fever rage unchecked, on the other hand, means exposing the fetus to harmful substances produced as the mother fights off her infection. Veronique Greenwood, Time, 10 Nov. 2025 Other types of filters include activated carbon, which removes odors, chemicals, and harmful gases, and UV-C light filters, which can kill bacteria and viruses. Karen Brewer Grossman, Southern Living, 9 Nov. 2025 Spirits Spirits are disembodied beings who are occasionally called upon to aid specific humans (usually witches), but can sometimes become harmful. Jordan Hoffman, Entertainment Weekly, 9 Nov. 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

Browse Nearby Words

Cite this Entry

“Harmful.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/harmful. Accessed 14 Nov. 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

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!