(1):
(n.) The dominion of an emperor; the territory or countries under the jurisdiction and dominion of an emperor (rarely of a king), usually of greater extent than a kingdom, always comprising a variety in the nationality of, or the forms of administration in, constituent and subordinate portions; as, the Austrian empire.
(2):
(n.) Supreme power; sovereignty; sway; dominion.
(3):
(n.) Any dominion; supreme control; governing influence; rule; sway; as, the empire of mind or of reason.