Tyranny is the opposite of freedom
Tyranny denies freedom, even when it is set in the name of freedom itself.
Few words have a more pejorative meaning than the terms "tyranny and tyrant." The word derives from Latin word “tyrannus”, and this last one derives in turn from the Greek word “τύραννος”. The Royal Spanish Academy defines it as:
"Person who gets the government of a State by breaking the law, especially if he rules it without justice and imposing his will" and also: "person who abuses of his power, superiority or strength in any issue or subject”, and also “who imposes that power and superiority to an extraordinary degree" simply.
But these are modern meanings that do not exactly match with the original meaning of the Greek word. In the long history of Greece there was a time when the primitive monarchical structures were disappearing because of the social and economic changes in the cities. In this development, the "democracy" or government of the people was their most remarkable creation, term that comes from the Greek people δῆμος (demos = people) and κράτος (kratos = power). Fifth century BC Athens is the best example of "democracy."
Sometimes, as the former royalty disappears, an individual person, a man, who comes out among the aristocratic families, gets the personal power and favors the social changes that are taking place at that moment, giving freedom to the people.
But also, in the struggles of the working classes against the aristocratic groups were very usual, since the sixth century, revolts in which an individual, often supported by the people or the army, took possession of the power and established a personal and absolutist rule system. Many of these "tyrants" were loved by the citizens due to their good policy which also favored the working classes and not just the aristocratic classes.
Thucydides is undoubtedly the most modern of the ancient historians for his critical sense and his strong commitment by telling us always the proved truth with objectivity. Speaking of tyranny, he tells us that at the beginning they had the royalty and that tyranny happened then as a result of the development of the power and wealthy of the Greek cities when they started to dominate the seas and set a lot of colonies (I, 13, 1). But he also says that tyrants only care about their personal situation, their own wealthy and their own person (I, 17).
As every absolutist and one-person power, tyranny tends and makes easy all kinds of excesses, so it is easy to understand the evolution of the meaning of the term, which was getting a negative meaning until the current one, which is absolutely pejorative.
From this point of view, it has a synonymous or very close meaning to other current terms such as dictator (originally Roman magistracy with exceptional powers), despot (also Greek word which means master, owner, headmaster and whose pejorative meaning is quite recent), satrap (head of a province of the Persian Empire) (see http://en.antiquitatem.com/satrap-persia-charlemagne-missi-dominici), totalitarian, authoritarian, etc.
Unfortunately the examples of tyrannies and dictatorships throughout the History of mankind are endless, even in the present times, in which there’s no doubt that the primary good of men and fundamental human right, after life, is freedom.
Neither is impossible nor absolutely uncommon to find that cruel tyrannies are established in the name of "freedom"; look how every tyrant always presents himself as a liberator and still nowadays they sometimes have the support of large groups of tyrannized citizens.