The Collaborative International Dictionary of English v.0.48:

Empire \Em"pire\, n. [F., fr. L. imperium a command,
   sovereignty, dominion, empire, fr. imperare. See Emperor;
   cf. Imperial.]
   1. Supreme power; sovereignty; sway; dominion. "The empire of
      the sea." --Shak.
      [1913 Webster]

            Over hell extend
            His empire, and with iron scepter rule. --Milton.
      [1913 Webster]

   2. 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.
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            Empire carries with it the idea of a vast and
            complicated government.               --C. J. Smith.
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   3. Any dominion; supreme control; governing influence; rule;
      sway; as, the empire of mind or of reason. "Under the
      empire of facts." --M. Arnold.
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            Another force which, in the Middle Ages, shared with
            chivalry the empire over the minds of men. --A. W.
                                                  Ward.
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   Celestial empire. See under Celestial.

   Empire City, a common designation of the city of New York.


   Empire State, a common designation of the State of New
      York.

   Syn: Sway; dominion; rule; control; reign; sovereignty;
        government; kingdom; realm; state.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Empire State \Empire State\
   New York; -- a nickname alluding to its size and wealth.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Empire State
    n 1: a Mid-Atlantic state; one of the original 13 colonies [syn:
         New York, New York State, Empire State, NY]