A constitution that combines elements of monarchy, aristocracy and democracy so that no single group can dominate; also called a mixed constitution.
In more detail
Aristotle described a polity or mixed constitution combining democratic and oligarchic features as the second-best system for most city-states. Polybius praised the Roman constitution as mixed, and the idea reappears in republican thought and in the separation of powers. Modern constitutions rarely claim the label but often rely on the same logic of checks.