Source : Webster's Revised Unabridged Dictionary (1913)

Imperium \Im*pe"ri*um\, n.; pl. {Imperia}. [L. See {Empire}.]
   1. Supreme power; absolute dominion; empire.

   2. (Law) The right to command, which includes the right to
      employ the force of the state to enforce the laws. It is
      one of the principal attributes of the executive power.