harmful
Americanadjective
adjective
Other Word Forms
Etymology
Origin of harmful
First recorded before 1000; Middle English; Old English hearmful; see harm, -ful
Explanation
Things that are harmful hurt people, or are likely to hurt them. Listening to loud music through headphones can be harmful to your hearing. Harmful is an adjective that comes in handy when you're talking about things that cause injury to someone or damage something. Burning coal can be harmful to the environment, and eating too much candy can be harmful for your teeth. Harmful words can hurt someone's feelings and harmful actions might put them in danger. The Old English hearm, "hurt, evil, or grief," is at the root of harmful.
Vocabulary lists containing harmful
Earth Day
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Unfavorable
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Harmful environments or substances can worsen your response to an exposure.
From The Wall Street Journal • Jan. 19, 2026
Harmful algae blooms had sickened marine life in each of the three years prior.
From Los Angeles Times • Sep. 17, 2025
Harmful algal blooms have been reported on every continent except Antarctica.
From Salon • Aug. 16, 2025
Harmful bacteria and algae can often spread more easily in warmer seawater, which isn't treated with cleaning chemicals like your local pool.
From BBC • Jul. 11, 2025
Harmful conditions within schoolrooms and on school grounds will not be neglected where pupils, teachers, school and family physicians, and parents set about to find and to remove the causes of physical defects.
From Civics and Health by Allen, William H.
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
