per·fi·dy 
(pûrfĭ-dē)
(pûrfĭ-dē)n. pl. per·fi·dies
1. Deliberate breach of faith; calculated violation of trust; treachery: "the fink, whose perfidy was equaled only by his gall" (Gilbert Millstein).
2. The act or an instance of treachery.
[Latin perfidia, from perfidus, treacherous : per-, to destruction; see PER- + fidēs, faith; see bheidh- in the Appendix of Indo-European roots.]