1751, "absolute power, unrestricted and unlimited authority," from French despotisme; see despot + -ism. By 1794 as "a political system based on an arbitrary government."
Tyranny is the abuse of absolute power, legal or usurped, and implies oppression. Despotism, in its earlier and still frequent meaning, does not necessarily imply either regard or disregard for the welfare of the subject; but there is also a tendency to give it essentially the same meaning as tyranny, using absolutism or autocracy where an unfavorable meaning is not intended. [Century Dictionary, 1897]