Separation of powers
Etymology
From “separation,” from Latin “separare,” “to pull apart,” + “powers.” The doctrine was crystallized by the French thinker Montesquieu in the eighteenth century, who argued that concentrating the making, enforcing, and judging of laws in one body was the very definition of tyranny — and that liberty required these functions be held apart.
noun phrase · /sep-uh-RAY-shun uv POW-urz/
The division of government into distinct branches — typically legislative, executive, and judicial — each with its own sphere.
What it names
Use it to name the structural safeguard of splitting the power to make, enforce, and judge laws among different hands.
Example
Housing the prosecutors under direct presidential control raised alarms about the separation of powers.
Related idea
Separation of powers is the static division into branches; checks and balances is the dynamic ability of each to restrain the others. Powers can be neatly separated on paper yet leave one branch unchecked in practice — the design needs both the walls and the levers that reach across them.