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
Derived 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.
And when it does, shipowners will still have to consider the risks of fiendish new challenges that the U.S.
From The Wall Street Journal • Apr. 11, 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
LosGothsCo held its Gothicumbia homecoming party on Aug. 15 at the Regent in downtown L.A., where a grimly fiendish procession of DJs spinning the sounds of cumbia, new Latin alternative, post-punk and rock en español.
From Los Angeles Times • Aug. 28, 2025
The Sidemen act as hosts and executive producers, putting their inmates through fiendish challenges that can see the £1m prize pot reduced.
From BBC • Jun. 3, 2024
While that lover sounded horrible indeed, if Mrs. Annie Thayer knew what he was up to, she was just as fiendish.
From "The Detective's Assistant" by Kate Hannigan
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.
