The Collaborative International Dictionary of English v.0.48:

authorities \authorities\ n.
   1. the organization that is the governing authority of a
      political unit.

   Syn: government, regime.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Authority \Au*thor"i*ty\, n.; pl. Authorities. [OE. autorite,
   auctorite, F. autorit['e], fr. L. auctoritas, fr. auctor. See
   Author, n.]
   1. Legal or rightful power; a right to command or to act;
      power exercised buy a person in virtue of his office or
      trust; dominion; jurisdiction; authorization; as, the
      authority of a prince over subjects, and of parents over
      children; the authority of a court.
      [1913 Webster]

            Thus can the demigod, Authority,
            Make us pay down for our offense.     --Shak.
      [1913 Webster]

            By what authority doest thou these things ? --Matt.
                                                  xxi. 23.
      [1913 Webster]

   2. Government; the persons or the body exercising power or
      command; as, the local authorities of the States; the
      military authorities. [Chiefly in the plural.]
      [1913 Webster]

   3. The power derived from opinion, respect, or esteem;
      influence of character, office, or station, or mental or
      moral superiority, and the like; claim to be believed or
      obeyed; as, an historian of no authority; a magistrate of
      great authority.
      [1913 Webster]

   4. That which, or one who, is claimed or appealed to in
      support of opinions, actions, measures, etc. Hence:
      (a) Testimony; witness. "And on that high authority had
          believed." --Milton.
      (b) A precedent; a decision of a court, an official
          declaration, or an opinion, saying, or statement
          worthy to be taken as a precedent.
      (c) A book containing such a statement or opinion, or the
          author of the book.
      (d) Justification; warrant.
          [1913 Webster]

                Wilt thou be glass wherein it shall discern
                Authority for sin, warrant for blame. --Shak.
          [1913 Webster]

WordNet (r) 3.0 (2006):

authorities
    n 1: the organization that is the governing authority of a
         political unit; "the government reduced taxes"; "the matter
         was referred to higher authorities" [syn: government,
         authorities, regime]