Source : Webster's Revised Unabridged Dictionary (1913)

Tyranny \Tyr"an*ny\, n. [OE. tirannye, OF. tirannie, F.
   tyrannie; cf. It. tirannia; Gr. ?, ?, L. tyrannis. See
   {Tyrant}.]
   1. The government or authority of a tyrant; a country
      governed by an absolute ruler; hence, arbitrary or
      despotic exercise of power; exercise of power over
      subjects and others with a rigor not authorized by law or
      justice, or not requisite for the purposes of government.

            ``Sir,'' would he [Seneca] say, ``an emperor mote
            need Be virtuous and hate tyranny.''  --Chaucer.

   2. Cruel government or discipline; as, the tyranny of a
      schoolmaster.

   3. Severity; rigor; inclemency.

            The tyranny of the open night's too rough For nature
            to endure.                            --Shak.

Source : WordNet®

tyranny
     n 1: a form of government in which the ruler is an absolute
          dictator (not restricted by a constitution or laws or
          opposition etc.) [syn: {dictatorship}, {absolutism}, {authoritarianism},
           {Caesarism}, {despotism}, {monocracy}, {one-man rule},
          {shogunate}, {Stalinism}, {totalitarianism}]
     2: dominance through threat of punishment and violence [syn: {absolutism},
         {despotism}]