Perfidy

From Latin perfidus ("faithless, treacherous, false"), from fides ("faith"); related to, for example, English fidelity.

Full definition of perfidy

(plural perfidies)

A state or act of violating faith or allegiance; violation of a promise or vow, or of trust reposed; faithlessness; treachery.
(legal) Specifically, in warfare, an illegitimate act of deception, such as using symbols like the Red Cross (symbol) or to gain proximity to an enemy for purposes of attack.

1921, Lassa Oppenheim, International law: a treatiseâ€Ž, Stratagems must be carefully distinguished strategy from perfidy, since the former are allowed, whereas the latter is prohibited.
1993, Leslie C. Green, The contemporary law of armed conflictâ€Ž, Abuse of a protective emblem amounts to perfidy and constitutes a war crime under the customary law of armed conflict.
2008, Sidney Axinn, A Moral Militaryâ€Ž, Ruses of war are legitimate so long as they do not involve treachery or perfidy on the part of the belligerent resorting to them.

1962, w:Barbara Tuchman, w, Germans could not get over the perfidy of it. It was unbelievable that the English, having degenerated to the stage where suffragettes heckled the Prime Minister and defied the police, were going to fight.
2000, Jul 17, Honda becomes chain letter victim, Honda Motor Co. is the latest victim of e-mail perfidy, which started when a phony chain letter promised that the automaker would give away free cars.
2008, Oct 16, McCain expected to make amends on Letterman show, Letterman roared about the perfidy of lying politicos.