The authority a government claims to suspend the ordinary rules in a crisis — to rule by decree, detain without normal trial, and override the limits that bind it in calm times. It is indispensable when the normal pace of law is too slow to save the state, and it is the oldest road by which free states have walked into tyranny.
In the Roman Republic, when invasion or revolt threatened the city, the Senate could call for extraordinary action and a consul would appoint a dictator: one magistrate raised above the rest, who could override the other magistrates, command the armies, and wield coercive power far beyond any ordinary office. He was called the dictator. The catch was time: his power lasted six months and then ended. The office was built to save the Republic and then disappear. Centuries later the same idea survives in many constitutions and legal systems — the power to break the glass in a crisis and rule without the usual limits. It can save a republic from destruction. It is also the tool by which republics have been destroyed, because the man who breaks the glass rarely wants to sweep it up. That is the permanent danger inside the necessity: the power taken to defend a free state is the same power that ends it.