empress vs woman

empress and woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
empress	Yes	No	No	No
woman	Yes	No	No	No

As nouns, woman is a hypernym of empress; that is, woman is a word with a broader meaning than empress:

Other hypernyms of empress include emperor, adult female.

empress (noun)	woman (noun)
a woman emperor or the wife of an emperor	women as a class
	an adult female person (as opposed to a man)
	a female person who plays a significant role (wife or mistress or girlfriend) in the life of a particular man