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an absolute monarch who rules with unlimited authority; by extension, any person with undisputed authority in a relationship or situation
Greek autokrates 'ruling by oneself'
1803, from French autocrate, from Greek autokrates "ruling by oneself, absolute, autocratic," from autos- "self" (see auto-) + kratia "rule," from kratos "strength, power" (see -cracy). First used by Robert Southey, with reference to Napoleon. An earlier form was autocrator (1789), used in reference to the Russian Czars. Earliest form in English is the fem. autocratress (1762).