A tyrant is a person who gets control of a country and then exploits the hell out of the people in it.
Tyranny is the system that keeps the tyrant in power, where he is free to commit genocide, have statues erected in his honor, and drink expensive liquor in peace while everyone else starves to death.
Some people are fond of using “tyranny” to describe anything they dislike about the government. Here’s a good test to see if they’re onto something:
If you live in a place where you can call your government tyrannical in public without fearing for your safety, congratulations! No tyranny is afoot.
Tyrants are terrifying and fear gets people’s attention. If you associate the horrors of the world’s worst dictatorships with, for example, the word “taxes,” you might start to confuse your feelings about group executions and mass graves with your feelings about increasing taxes for rich people. So listen carefully and watch what you say. You’re our only hope.