fiendish
Americanadjective
adjective
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of or like a fiend
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diabolically wicked or cruel
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informal extremely difficult or unpleasant
a fiendish problem
Other Word Forms
Etymology
Origin of fiendish
Explanation
To be fiendish is to be cruel or evil. You might choose not to watch horror films — or soap operas — if you're not a fan of seeing people do fiendish things to each other. Fiendish behavior is terrible and vicious, and fiendish people behave without kindness or conscience. An informal, less serious way to use the adjective is to mean "complicated or difficult." You might, for example, describe your fiendish calculus exam or rave about the fiendish plot in your favorite book. Fiendish comes from fiend, "evil spirit," with its Old English root feogan, "to hate."
Vocabulary lists containing fiendish
Coraline
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"The Witches" by Roald Dahl, Chapters 6–11
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The Egypt Game
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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.
To make up for it, he pulled out a completely different jumping pass on the fly, starting with a different quad—-and then landed another fiendish combination.
From The Wall Street Journal ● Feb. 9, 2026
That is good news for Inter who have a fiendish run of fixtures to close their league phase campaign, including clashes at the San Siro with Liverpool and Premier League leaders Arsenal.
From Barron's ● Nov. 5, 2025
Easy enough - except our celebrities had to navigate through a fiendish array of red laser beams, all pointing at awkward angles, meaning the most nimble had the easiest time of it.
From BBC ● Oct. 30, 2025
Ritter’s second novel is a fiendish tale of trouble in paradise.
From Los Angeles Times ● Mar. 21, 2025
A film of red dust on his hair and eyebrows and the tip of his strong chin gave him a fiendish look untrue to his nature.
From "The Poisonwood Bible" by Barbara Kingsolver
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.
