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[per-fid-ee-uh s] /pərˈfɪd i əs/
deliberately faithless; treacherous; deceitful:
a perfidious lover.
Origin of perfidious
First recorded in 1590-1600, perfidious is from the Latin word perfidiōsus faithless, dishonest. See perfidy, -ous
Related forms
perfidiously, adverb
perfidiousness, noun
unperfidious, adjective
unperfidiously, adverb
unperfidiousness, noun
false, disloyal; unfaithful, traitorous.
faithful. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for perfidiously
Historical Examples
  • Taking advantage of his absence, they perfidiously vilified him to the king.

  • (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
  • Thus we learned the dismal place to which your noble daughter had been so perfidiously ensnared.

    My Novel, Complete Edward Bulwer-Lytton
  • But the Prefet's party had perfidiously made thirty of its most devoted adherents vote for Albert, so as to deceive the enemy.

    Albert Savarus Honore de Balzac
  • For it was long believed that Delauney had admitted the people into the first court, and then had perfidiously shot them down.

    Lectures on the French Revolution John Emerich Edward Dalberg-Acton
  • On the testimony of his own letters it is clear he did not mind how tortuously and perfidiously he worked.

    Sir Walter Ralegh William Stebbing
  • His mistress loved him as long as his money lasted; when he had no more to throw away upon her she perfidiously betrayed him.

British Dictionary definitions for perfidiously


guilty, treacherous, or faithless; deceitful
Derived Forms
perfidiously, adverb
perfidiousness, 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
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Word Origin and History for perfidiously



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

Online Etymology Dictionary, © 2010 Douglas Harper
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