perfidy

1 lack of faithfulness especially to one's husband or wife he decided to forgive his wife's perfidy, choosing to ascribe it to a moment of uncharacteristic weakness Synonyms disloyalty, faithlessness, falseness, falsity, inconstancy, perfidiousness, infidelity, unfaithfulnessRelated Words adultery; betrayal, double-cross, double-dealing, duplicity, sellout, treachery, treason; deceit, deception, lyingNear Antonyms staunchness, steadfastness; dependability, reliability; honesty, trustworthinessAntonyms allegiance, constancy, devotedness, devotion, faith, faithfulness, fealty, fidelity, loyalty

2 the act or fact of violating the trust or confidence of another the full cost—both in compromised intelligence and in human life—of the double agent's perfidy is not yet known Synonyms backstabbing, business, disloyalty, double cross, faithlessness, falseness, falsity, infidelity, betrayal, sellout, treachery, treason, two-timing, unfaithfulnessRelated Words abandonment, desertion; deceit, deception, double-dealing, duplicity, guile, two-facedness; fraud, informing, lying, snitching, talebearing, trickeryNear Antonyms dependability, reliability, trustworthiness; defense, protection, safeguard, shieldAntonyms allegiance, devotion, faithfulness, fealty, fidelity, loyalty, staunchness, steadfastness