double cross

This term carries a strong connotation of calculated treachery and opportunistic betrayal. It is specifically used when two or more people have entered into a secret, often illicit, agreement, and one party breaks that trust to secure a better deal or avoid punishment. It differs from a general lie or a simple betrayal because it implies a pre-existing pact of mutual deception.

In terms of register, it is common in crime fiction, espionage thrillers, and casual conversation. While the noun form is countable, the verb form is often written as a single word (double-cross) or two words; however, the semantic focus remains on the reversal of loyalty within a conspiracy.