1650s, "independent power, self-sustained power," from French autocratie, from Greek autokrateia "ruling by oneself," noun of state from autokrates (see autocrat). Meaning "absolute government, supreme political power" is recorded from 1855.
A system of government in which supreme political power is held by one person. (Compare constitutional monarchy, democracy, and oligarchy.)
Note: Iraq under Saddam Hussein is an autocracy.