heiress vs heir

heiress and heir both are nouns.

Word	Noun	Adjective	Verb	Adverb
heiress	Yes	No	No	No
heir	Yes	No	No	No

As nouns, heir is a hypernym of heiress; that is, heir is a word with a broader meaning than heiress:

heiress: a female heir
heir: a person who is entitled by law or by the terms of a will to inherit the estate of another

Other hypernyms of heiress include heritor, inheritor, adult female, woman.

heiress (noun)	heir (noun)
a female heir	a person who is entitled by law or by the terms of a will to inherit the estate of another
	a person who inherits some title or office