Complete tyranny can only come when the ruling power has the willingness of those being ruled. When a group of dominated persons are ignorant and unaware of the actions of its government it is then that tyranny can occur. Tyranny is defined as a cruel use of power. If citizens are aware of their rights and their own power as an individual and as a group, do you think a small group known as the government can take complete control of them? The odds are in favor of the educated public. However, when one is not aware of their rights or does not have the knowledge to recognize when it is that their government is crossing the line, then they have already lost the battle and may as well surrender now.
History books showcase Cicero's point, politically speaking. African slaves in America were not allowed to read or write - they were not allowed to be educated.
It was feared that once educated, the slaves might begin to communicate with slaves from surrounding plantations and organize a revolt against their rules - the slave masters. The only way for these slave masters to maintain sovereignty was to keep the prisoners captives of ignorance.
Another example can be found in the European Jewish ghettos during WWII. The Jews were not allowed to know what the Nazi government was up to. They were repeatedly lied to about the actual actions of the government. Surely if they had known what was in store for them, there would have been a much stronger effort to prevent it. The few, brave non-Jews who tried to help soon found their voices suppressed.
Tyranny can be found outside of government also. Yes, Webster is careful to point out that tyranny applies to government in his definition, but...