Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

            By what authority doest thou these things ? --Matt.
                                                  xxi. 23.

   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.]

   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.

   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.

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

Source : WordNet®

authority
     n 1: the power or right to give orders or make decisions; "he has
          the authority to issue warrants"; "deputies are given
          authorization to make arrests" [syn: {authorization}, {authorisation},
           {dominance}, {say-so}]
     2: (usually plural) persons who exercise (administrative)
        control over others; "the authorities have issued a
        curfew"
     3: an expert whose views are taken as definitive; "he is an
        authority on corporate law"
     4: freedom from doubt; belief in yourself and your abilities;
        "his assurance in his superiority did not make him
        popular"; "after that failure he lost his confidence";
        "she spoke with authority" [syn: {assurance}, {self-assurance},
         {confidence}, {self-confidence}, {sureness}]
     5: an administrative unit of government; "the Central
        Intelligence Agency"; "the Census Bureau"; "Office of
        Management and Budget"; "Tennessee Valley Authority" [syn:
         {agency}, {federal agency}, {government agency}, {bureau},
         {office}]
     6: official permission or approval; "authority for the program
        was renewed several times" [syn: {authorization}, {authorisation},
         {sanction}]
     7: an authoritative written work; "this book is the final
        authority on the life of Milton"