What noun means "rule" or "law"?

The term "principle" fits the definition of "rule" or "law" because it refers to a fundamental truth or proposition that serves as the foundation for a system of belief or behavior. Principles guide behavior and decision-making, often serving as the unwritten rules that individuals or organizations follow in order to maintain order and establish expectations.

In a broader context, principles can encompass legal, ethical, or moral frameworks that dictate how individuals and groups should behave. This aligns closely with the concept of a "rule" or "law," which provides guidelines for conduct within a given context.

Other terms in the choices do not encapsulate the definition as completely. "Principal" typically refers to an individual in charge, "debt" represents an obligation or liability, and "mandate" refers to an authoritative command or instruction, rather than a foundational rule or law.