tyrannical vs authoritarian

tyrannical is not a noun while authoritarian is a noun.

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

As adjectives, tyrannical and authoritarian are synonyms defined as:

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

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

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

tyrannical (adjective)	authoritarian (adjective)
marked by unjust severity or arbitrary behavior	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