Per″fi‐dy (pẽr″fĭ‐dy̆), n.; pl.Perfidies (–dĭz). [L. perfidia, fr. L. perfidus faithless; per (cf. Skr. parā away) + fides faith: cf. F. perfidie. See Faith.] The act of violating faith or allegiance; violation of a promise or vow, or of trust reposed; faithlessness; treachery.
The ambition and perfidy of tyrants. Macaulay.
His perfidy to this sacred engagement. DeQuincey.