Source : Webster's Revised Unabridged Dictionary (1913)

Perfidy \Per"fi*dy\ (p[~e]r"f[i^]*d[y^]), n.; pl. {Perfidies}
   (-d[i^]z). [L. perfidia, fr. L. perfidus faithless; per (cf.
   Skr. par[=a] 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.