tyrant vs dictator

tyrant and dictator both are nouns.

Word	Noun	Adjective	Verb	Adverb
tyrant	Yes	No	No	No
dictator	Yes	No	No	No

As nouns, dictator is a hypernym of tyrant; that is, dictator is a word with a broader meaning than tyrant:

Other hypernyms of tyrant include potentate.

tyrant (noun)	dictator (noun)
a cruel and oppressive dictator	a ruler who is unconstrained by law
any person who exercises power in a cruel way	a person who behaves in a tyrannical manner
in ancient Greece, a ruler who had seized power without legal right to it	a speaker who dictates to a secretary or a recording machine