Answer:
The main difference in the concept of tyranny of the ancient Greeks and the one that Americans have today lies in the moment in which the tyrant exercises violence: for the Greeks, the tyrant was that ruler who acceded to his position of leadership through violence (be it through an overthrow, or a civil war, or a military uprising, etc.), that is, he was the one who illegitimately acceded to a position of power, avoiding democratic elections. But this Greek tyrant did not necessarily have to be violent towards his citizens; even some tyrants have been very well pondered by their people, being popular and loved.
Instead, the current concept of a tyrant has inverted the definition: today, a leader is considered to be a tyrant is the one who, having gained power illegally or not (may even have gained access through democratic means, such as Hugo Chavez in Venezuela), exercises violence against its citizens during its government, be it physical violence, as well as political or even economic violence.
