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From Middle French perfidie, from Latin perfidus (faithless, treacherous, false), from fides (faith); related to, for example, English fidelity.


  • (UK) IPA(key): /ˈpɜː.fɪ.di/
  • (file)
  • (US) IPA(key): /ˈpɝ.fɪ.di/


perfidy (countable and uncountable, plural perfidies)

  1. A state or act of violating faith or allegiance; violation of a promise or vow, or of trust.
    Synonyms: treachery, betrayal
  2. (international law, in warfare) An illegitimate act of deception, such as using symbols like the Red Cross or white flag in a false claim of surrender to gain proximity to an enemy for purposes of attack.
    • 1921, Lassa Oppenheim with Ronald Francis Roxburgh, International law: a treatise, page 229:
      Stratagems must be carefully distinguished strategy from perfidy, since the former are allowed, whereas the latter is prohibited.
    • 1993, Leslie C. Green, The contemporary law of armed conflict, page 89:
      Abuse of a protective emblem amounts to perfidy and constitutes a war crime under the customary law of armed conflict.
    • 2008, Sidney Axinn, A Moral Military, page 84:
      Ruses of war are legitimate so long as they do not involve treachery or perfidy on the part of the belligerent resorting to them.
    • 2012 June 5, Patrick Lin, Neil Rowe, Fritz Allhoff, “Is It Possible to Wage a Just Cyberwar?”, in The Atlantic[1]:
      Cyberattacks almost inevitably involve an element of deception, such as tricking a user to click on a malicious link. So, to what extent could cyberattacks count as perfidy and therefore be illegal given international humanitarian law?
  3. A state or act of deceit.
    • 1962, Barbara Wertheim Tuchman, The Guns of August, page 154:
      Germans could not get over the perfidy of it. It was unbelievable that the English, having degenerated to the stage where suffragettes heckled the Prime Minister and defied the police, were going to fight.
    • 2000 July 17, “Honda becomes chain letter victim”, in eWeek:
      Honda Motor Co. is the latest victim of e-mail perfidy, which started when a phony chain letter promised that the automaker would give away free cars.
    • 2008 October 16, “McCain expected to make amends on Letterman show”, in Los Angeles Times:
      Letterman roared about the perfidy of lying politicos.



Related terms[edit]