mill-girl vs factory worker

mill-girl and factory worker both are nouns.

Word	Noun	Adjective	Verb	Adverb
mill-girl	Yes	No	No	No
factory worker	Yes	No	No	No

As nouns, factory worker is a hypernym of mill-girl; that is, factory worker is a word with a broader meaning than mill-girl:

Other hypernyms of mill-girl include fille, girl, miss, missy, young lady, young woman, mill-hand.

mill-girl (noun)	factory worker (noun)
a girl who works in a mill	a workman in a mill or factory