authoritarian vs tyrannic

authoritarian is a noun but tyrannic is not a noun.

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

As adjectives, authoritarian and tyrannic are synonyms defined as:

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

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

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

authoritarian (adjective)	tyrannic (adjective)
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