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
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.
By replacing outdated and harmful practices, HMS aims to empower brands, laundries and mills to achieve both environmental and commercial goals. Angela Velasquez, Sourcing Journal, 29 Sep. 2025 Typically caused by a sensitive immune system — which confuses innocuous bacteria for harmful pathogens — symptoms include fever, fatigue, abdominal pain, nausea, diarrhea, loss of appetite and weight loss, anemia, skin changes, arthritis and more. Vanessa Etienne, PEOPLE, 29 Sep. 2025 Tech companies sporadically work with local police to track and deplatform harmful accounts, law enforcement sources say. Avery Schmitz, CNN Money, 29 Sep. 2025 When OpenAI and Anthropic evaluated each other's models over the summer, OpenAI reported Claude was less likely to engage in sycophantic and harmful behaviors than ChatGPT. Emily Forlini, PC Magazine, 29 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

Browse Nearby Words

Cite this Entry

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