merciless
Americanadjective
adjective
Other Word Forms
Etymology
Origin of merciless
First recorded in 1300–50; Middle English mercyles; see mercy, -less
Explanation
Use the adjective merciless to describe someone who acts in a cruel, heartless way. You could accuse your rabbit-hunting brother of being merciless. Merciless is the antonym, or opposite, of "merciful." If a person shows no mercy or pity, she is merciless. This can describe a cruelly violent person, or it can be more figurative: "The torrential rain was merciless, pouring down on the wedding party as they ran to take cover." The root word is mercy, which comes from the French merci, "reward, gift, or kindness."
Vocabulary lists containing merciless
Hamilton
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Schooled
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Theodore Roosevelt on "The Man with the Muck Rake" (1906)
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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.
The heat index -- which measures how hot it feels based on temperature and humidity combined -- was even more merciless.
From Barron's • Jul. 2, 2026
At the Australian Open in 2025, he was outclassed in a merciless performance by Jannik Sinner that left Zverev saying he felt mentally "empty" a few months later.
From BBC • Jun. 7, 2026
Martin Amis, a merciless observer of foibles, puts one writer’s envy of another at the heart of “The Information.”
From The Wall Street Journal • Dec. 5, 2025
Nevertheless, she remains as statuesque and merciless as Weaver was onscreen.
From Los Angeles Times • Oct. 28, 2025
His voice drifted to me again, from about the same distance, soft and merciless.
From "Black Like Me" by John Howard Griffin
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.
