perfidious
Americanadjective
adjective
Other Word Forms
Etymology
Origin of perfidious
First recorded in 1530–40; from Latin perfidiōsus “faithless, dishonest”; cf. perfidy, -ous
Explanation
If someone accuses you of being perfidious, you should probably be offended — it means underhanded, treacherous, deceitful — even evil. If you betray people often, you're perfidious: traitors are extremely perfidious. Besides betrayal, this word implies lying and maybe other kinds of awful behavior, like stealing and taking bribes. Everyone tries to avoid perfidious people. Perfidious is kind of an old-fashioned word, but being perfidious will never go out of style, unfortunately.
Vocabulary lists containing perfidious
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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.
Samuel Pepys knew him; the British diarist thought him “a perfidious rogue.”
From The Wall Street Journal ● Mar. 11, 2026
The head of one of them, who preferred to remain anonymous, described it as a "perfidious and effective" strategy.
From Barron's ● Nov. 1, 2025
“If the initial findings are confirmed, it will be a perfidious attack on our electricity infrastructure,” Stübgen said.
From Seattle Times ● Mar. 5, 2024
He also exerts a malignant perfidious influence over people who are vulnerable to such energy and temptations, but for whatever reason have not yet fully surrendered to them.
From Salon ● Feb. 2, 2024
There was an element of chauvinism in this—the French supported their own champion and rejected the ideas of the perfidious Englishman, while Newton was, of course, very much a prophet honoured in his own country.
From "The Scientists" by John Gribbin
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.
