the.com/federalism

means A system of government where power is split between a central authority and regional units (like states or provinces), each sovereign in its own sphere.

from From Latin 'foedus' (genitive 'foederis'), meaning covenant, treaty, or league — the same root gives us 'federate' and 'confederacy.' The idea was Rome's: a bond between parties who stay distinct but bind themselves by agreement. The word entered political theory in earnest in the late 18th century, when American framers debating a 'more perfect union' needed a term for power shared rather than surrendered — neither one nation nor a loose alliance, but a covenant between layers of government.