tyranny

Short definition from Wiktionary

Noun

1. 1
   A government in which a single ruler (a tyrant) has absolute power, or this system of government; especially, one that acts cruelly and unjustly.
2. 2
   The office or jurisdiction of an absolute ruler.
3. 3
   Absolute power, or its use.
4. 4
   A system of government in which power is exercised on behalf of the ruler or ruling class, without regard to the wishes of the governed.
5. 5
   Extreme severity or rigour.