harm·​ful | \ˈhärm-fəl \

Definition of harmful 

: of a kind likely to be damaging : injurious

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Other Words from harmful

harmfully \ ˈhärm-​fə-​lē \ 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

Cyanobacteria thrives in water above 68 degrees and as long as nutrients are available can continue to grow, said Tim Davis, a Bowling Green State University molecular microbiologist who specializes in harmful algae blooms. Jenny Staletovich, miamiherald, "Political muscle halts release of Lake O's foul water. The reprieve won't last long," 9 July 2018 Farm runoff is considered a major cause of harmful algal blooms in our lakes and rivers. Emily Hopkins, Cincinnati.com, "Your produce is less healthy than it was 70 years ago. These farmers might change that," 4 July 2018 Most of the remaining outbreaks were caused by parasites transmitted by birds present in recreational waters, toxins and chemicals or harmful algal blooms, the report says. Jamie Ducharme, Time, "Why July Is the Most Dangerous Month To Go Swimming," 28 June 2018 Likewise, since announcing the ban on CFC-11, China has demanded that companies switch to less harmful chemicals. Chris Buckley, New York Times, "In a High-Stakes Environmental Whodunit, Many Clues Point to China," 24 June 2018 These false associations are especially harmful (and pointless) if the superstition has nothing to do with the mechanics of the sport — the difference between taping an ankle a certain way and wearing a lucky sock. Danielle Lerner, The Courier-Journal, "Superstitions are supersized for Justify's Triple Crown run," 4 June 2018 Every part of poison ivy can be harmful, from the leaves to the branches and base. Timothy Dahl, Popular Mechanics, "How to Get Rid of Poison Ivy," 4 June 2018 Vehicles release harmful chemicals that add to air pollution. Max Londberg, kansascity, "KC's air will be unhealthy for kids, outdoor enthusiasts and older adults Thursday," 30 May 2018 This year's winners include concepts for elegant dinner parties, online marketplaces and an app identifying potentially harmful chemicals in products. Jane Wooldridge, miamiherald, "And the 2018 Miami Herald Business Plan Challenge winners are ..... | Miami Herald," 3 May 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'harmful.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of harmful

14th century, in the meaning defined above

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Dictionary Entries near harmful

harm's way







Statistics for harmful

Last Updated

11 Nov 2018

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Time Traveler for harmful

The first known use of harmful was in the 14th century

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More Definitions for harmful



English Language Learners Definition of harmful

: causing or capable of causing damage or harm


harm·​ful | \ˈhärm-fəl \

Kids Definition of harmful

: causing or capable of causing harm : injurious Keep harmful substances away from children.

Other Words from harmful

harmfully \ -​fə-​lē \ adverb



Legal Definition of harmful 

: of a kind likely to cause harm

Other Words from harmful

harmfully adverb
harmfulness noun

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More from Merriam-Webster on harmful

Thesaurus: All synonyms and antonyms for harmful

Spanish Central: Translation of harmful

Nglish: Translation of harmful for Spanish Speakers

Britannica English: Translation of harmful for Arabic Speakers

Comments on harmful

What made you want to look up harmful? Please tell us where you read or heard it (including the quote, if possible).


playful or foolish behavior

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