From Longman Dictionary of Contemporary Englishperfidyper‧fi‧dy /ˈpɜːfədi $ ˈpɜːr-/ noun [uncountable] literary TRICK/DECEIVEwhen someone is not loyal to another person who trusts them SYN treachery
Examples from the Corpus
perfidy• On trips organised for food writers, public perfidy is a popular lament.• Anyway, they've seized on this legal brouhaha as an example of Albion's perfidy, so to speak.• After dinner, they lined the bar, talking loudly about the perfidy of Highlanders and bemoaning their ten-mile, fishless walk.• Young Zuwaya talked with anger and shock, lips and hands trembling, about the perfidy of the Magharba.• When the Seminoles and blacks responded to this perfidy by refusing to cooperate in their removal, Jesup renewed warfare.• But can you live with your perfidy? 