harmful

1 of 2

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

harmfulness

2 of 2

noun

harm·​ful·​ness
plural -es
: the quality or state of being harmful

Synonyms of harmful

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Adjective

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Examples of harmful in a Sentence

Adjective 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.
Adjective
Fires that burn at low temperature produce more harmful gases than hot fires. — Eric Niiler, Los Angeles Times, 6 July 2026 Think of it as skincare in disguise, locking in at least 12 hours of moisture while shielding you from harmful UV rays. — Tanya Sharma, InStyle, 4 July 2026 Meta said the changes were designed to reduce exposure to potentially harmful content and create safer online experiences for younger users. — Larry Magid, Mercury News, 2 July 2026 The agency is also monitoring for cyanobacteria, formerly known as blue-green algae, which can form harmful algal blooms that pose risks to people and animals. — Madison Smalstig july 3, Sacbee.com, 3 July 2026 See All Example Sentences for harmful

Word History

First Known Use

Adjective

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 10 Jul. 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

More from Merriam-Webster on harmful

Nglish: Translation of harmful for Spanish Speakers

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