perfidy
Americannoun
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deliberate breach of faith or trust; faithlessness; treachery.
perfidy that goes unpunished.
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an act or instance of faithlessness or treachery.
noun
Synonym Usage
See disloyalty.
Etymology
Origin of perfidy
1585–95; < Latin perfidia faithlessness, equivalent to perfid ( us ) faithless, literally, through (i.e., beyond the limits of ) faith ( per- per- + fid ( ēs ) faith + -us adj. suffix) + -ia -y 3
Explanation
If you shared your most embarrassing secrets with a friend who then told them to everyone he knows, his betrayal could be described as perfidy. The noun perfidy means "deceitfulness" or "treachery," so it's not just being mean, but deliberately betraying a trust. The Latin root of perfidy is made up of per, or "through," and fidem, or "faith." So in order for perfidy to happen, there has to have first been a sense of faith in place, which was then broken or betrayed.
Vocabulary lists containing perfidy
The Declaration of Independence
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A Web of Lies
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Excerpt from "The Declaration of Independence"
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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.
He has persisted in insulting the leaders of these countries for failing to bail him out of his jam, writing long screeds on social media that rail against their alleged perfidy.
From Salon • Mar. 19, 2026
Jack soon learns, in Robert Penn Warren’s saga of perfidy and corruption, that Gov. Stark is right.
From The Wall Street Journal • Oct. 23, 2025
Bristling and increasingly convinced of Western perfidy and decadence, he was in many respects a changed man.
From Seattle Times • Mar. 26, 2022
He was everything she could desire, Till his perfidy filled her with ire.
From Washington Post • Sep. 2, 2021
Isn’t it ridiculous to think that a mouse could ever forgive anyone for such perfidy?
From "The Tale of Despereaux: Being the Story of a Mouse, a Princess, Some Soup and a Spool of Thread" by Kate DiCamillo
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.
