autocratic vs authoritarian

autocratic is not a noun while authoritarian is a noun.

Word	Noun	Adjective	Verb	Adverb
autocratic	No	Yes	No	No
authoritarian	Yes	Yes	No	No

As adjectives, autocratic and authoritarian are synonyms defined as:

autocratic and authoritarian: characteristic of an absolute ruler or absolute rule; having absolute sovereignty

Other synonyms of autocratic include despotic, dictatorial, tyrannic, tyrannical.

autocratic (noun)	authoritarian (noun)
	a person who behaves in a tyrannical manner

autocratic (adjective)	authoritarian (adjective)
offensively self-assured or given to exercising usually unwarranted power	expecting unquestioning obedience
characteristic of an absolute ruler or absolute rule; having absolute sovereignty	characteristic of an absolute ruler or absolute rule; having absolute sovereignty