Treachery
Part of speech: noun
Definition: Deliberate, often calculated, disregard for trust or faith. The act of violating the confidence of another, usually for personal gain. Treason.
Example sentence: One of the most depressing aspects of the whole Brexit debate has been the rush to instant judgment about the motives of MPs and others and the readiness to accuse others of treachery or betrayal.
Perfidy
Part of speech: noun
Definition: A state of act of violating faith or allegiance; violation of a promise or vow, or of trust reposed; faithlessness; treachery.Specifically, in warfare, an illegitimate act of deception, such as using symbols like the Red Cross or white flag to gain proximity to an enemy for purposes of attack.A state or act of deceit.