From Middle French infidélité, from Latin infidelitas. Equivalent to infidel +‎ -ity.


  • IPA(key): /ˌɪnfɪˈdɛlɪti/


infidelity (countable and uncountable, plural infidelities)

  1. Unfaithfulness in a marriage or an intimate relationship: practice or instance of having a sexual or romantic affair with someone other than one's spouse, without the consent of the spouse.
    • 2013, William G. Staples, Everyday Surveillance: Vigilance and Visibility, →ISBN, page 155:
      Your friends tell you rumors about your girlfriend's infidelity or you remember being broken up around the time the baby was conceived.
  2. Unfaithfulness in some other moral obligation.
    • 1937, Arnold Oskar Meyer, England in German opinion throughout the centuries, page 6:
      It was disastrous that England's infidelity towards Frederick the Great — which no one, not even a German, condemned more strongly than did William Pitt — had to affect one of the most popular heroes of our national history.
  3. Lack of religious belief.
    • 1674, Seth Ward, Seven Sermons
      The means used to this purpose are partly didactical, and partly protreptical; demonstrating the truth of the gospel, and then urging the professors of those truths to be stedfast[sic] in the faith, and to beware of infidelity.



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