authoritarian vs autocratic

authoritarian is a noun but autocratic is not a noun.

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

As adjectives, authoritarian and autocratic are synonyms defined as:

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

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

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

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