bachelor girl vs woman

bachelor girl and woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
bachelor girl	Yes	No	No	No
woman	Yes	No	No	No

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

Other hypernyms of bachelor girl include adult female.

bachelor girl (noun)	woman (noun)
a young unmarried woman who lives alone	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