oppressor vs dictator

oppressor and dictator both are nouns.

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

As nouns, dictator is a hyponym of oppressor; that is, dictator is a word with a more specific, narrower meaning than oppressor:

oppressor (noun)	dictator (noun)
a person of authority who subjects others to undue pressures	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