The two brothers had a pact to back each other up in front of their parents.
Tips
usage
Originally a real military/diplomatic term. In modern usage, the figurative sense (suspects or accomplices coordinating stories) is far more common, often with a tongue-in-cheek tone for kids and siblings.
history
Modern compound coined to render the European concept; appears in 曾朴's late-Qing novel 《孽海花》 about the late-19th-century treaty system.
