Star-empire

The term star-empire, also stylised as star empire, applied to an empire encompassing more than one planet, even extending into interstellar territory to conquer other star systems.

Both the Manussan Empire and the Sumaran Empire had been two great star-empires, both with Manussa as the ruling world, before the empires fell and Manussa became a colony of the "all-powerful" Federation of Three Worlds. (PROSE: Snakedance)

The First Skonnan Empire had been a once-great star empire, dominating a hundred worlds and controlling a hundred star systems, before it collapses into in-fighting and civil war. (PROSE: Doctor Who and the Horns of Nimon)