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  1. deliberately faithless; treacherous; deceitful: a perfidious lover.
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Origin of perfidious

First recorded in 1590–1600, perfidious is from the Latin word perfidiōsus faithless, dishonest. See perfidy, -ous
Related formsper·fid·i·ous·ly, adverbper·fid·i·ous·ness, nounun·per·fid·i·ous, adjectiveun·per·fid·i·ous·ly, adverbun·per·fid·i·ous·ness, noun

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Antonyms for perfidious

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for perfidiousness

infidelity, fraud, disloyalty, falseness, disbelief, falsity, dishonesty, treason, betrayal, perfidy, doubt, unfaithfulness, skepticism, treachery, inconstancy

Examples from the Web for perfidiousness

Contemporary Examples of perfidiousness

Historical Examples of perfidiousness

British Dictionary definitions for perfidiousness


  1. guilty, treacherous, or faithless; deceitful
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Derived Formsperfidiously, adverbperfidiousness, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for perfidiousness



1590s, from Latin perfidiosus "treacherous," from perfidia (see perfidy). Related: Perfidiously; perfidiousness.

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Online Etymology Dictionary, © 2010 Douglas Harper