postmistress vs woman

postmistress and woman both are nouns.

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

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

Other hypernyms of postmistress include postmaster, adult female.

postmistress (noun)	woman (noun)
a woman postmaster	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