tyranny

n. unchecked use of power and authority; government in which all power is vested in one absolute dictator; despotic or oppressive act; domineering or despotic behavior

n. oppression, coercive power (esp. by a government); position or role of a tyrant; strict and harsh condition imposed by an external person or force

In modern usage a tyrant is a single ruler holding vast, if not absolute power through a state or in an organization. The term carries connotations of a harsh and cruel ruler who places his/her own interests or the interests of a small oligarchy over the best interests of the general population which they govern or control. This mode of rule is referred to as tyranny. Many individual rulers or government officials are accused of tyranny, with the label almost always a matter of controversy.
See more at Wikipedia.org...

Noun
1. a form of government in which the ruler is an absolute dictator (not restricted by a constitution or laws or opposition etc.)
(synonym) dictatorship, absolutism, authoritarianism, Caesarism, despotism, monocracy, one-man rule, shogunate, Stalinism, totalitarianism
(hypernym) autocracy, autarchy
(hyponym) police state
2. dominance through threat of punishment and violence
(synonym) absolutism, despotism
(hypernym) dominance, ascendance, ascendence, ascendancy, ascendency, control

(n.)
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.
  

(n.)
Severity; rigor; inclemency.
  

(n.)
Cruel government or discipline; as, the tyranny of a schoolmaster.
  

TYRANNY, TYRANT - The violation of those laws which regulate the division and the exercises of the sovereign power of the state. It is a violation of its Constitution.

TYRANT - The chief magistrate of the state, whether legitimate or otherwise, who violates the Constitution to act arbitrarily contrary to justice.

The term tyrant and usurper, are sometimes used as synonymous, because usurpers are almost always tyrants; usurpation is itself a tyrannical act, but properly speaking, the words usurper and tyrant convey different ideas. A king may become a tyrant, although legitimate, when he acts despotically; while a usurper may cease to be a tyrant by governing according to the dictates of justice.

This term is sometimes applied to persons in authority who violate the laws and act arbitrarily towards others.
   

This entry contains material from Bouvier's Legal Dictionary, a work published in the 1850's.