noun
galactic empire
Used in science fiction to refer to a vast interstellar empire spanning a galaxy.
そのSF小説では、銀河帝国が崩壊しつつある。
In that science fiction novel, the galactic empire is collapsing.
Compound of 銀河 (ginga, 'galaxy') and 帝国 (teikoku, 'empire'). A straightforward modern coinage for science fiction contexts.