tomboy vs young woman

tomboy and young woman both are nouns.

Word	Noun	Adjective	Verb	Adverb
tomboy	Yes	No	No	No
young woman	Yes	No	No	No

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

Other hypernyms of tomboy include fille, girl, miss, missy, young lady.

tomboy (noun)	young woman (noun)
a girl who behaves in a boyish manner	a young female