Big Brother vs dictator

Big Brother and dictator both are nouns.

Word	Noun	Adjective	Verb	Adverb
Big Brother	Yes	No	No	No
dictator	Yes	No	No	No

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

Other hypernyms of Big Brother include authoritarian.

Big Brother (noun)	dictator (noun)
a totalitarian leader and invader of privacy	a ruler who is unconstrained by law
	a person who behaves in a tyrannical manner
	a speaker who dictates to a secretary or a recording machine