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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

Synonyms for perfidious

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Antonyms for perfidious

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

Examples from the Web for perfidiously

Historical Examples of perfidiously

  • Taking advantage of his absence, they perfidiously vilified him to the king.

    Chambers's Edinburgh Journal, No. 458


  • (Perfidiously to the Marchioness) Look out, you know he's becoming dangerous for you.

    Three Plays

    Luigi Pirandello

  • Perfidiously, they only sought time to regain their strength.

  • He had been perfidiously treated, and Albuquerque now, in 1511, appeared before the city to call the monarch to account.

  • This man entered into a conspiracy with the English, to betray to them the King to whom he had perfidiously sworn allegiance.

    Joseph Bonaparte

    John S. C. Abbott

British Dictionary definitions for perfidiously


  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 perfidiously



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

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Online Etymology Dictionary, © 2010 Douglas Harper