millionairess vs woman

millionairess and woman both are nouns.

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

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

Other hypernyms of millionairess include have, rich person, wealthy person, adult female.

millionairess (noun)	woman (noun)
a woman millionaire	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