young lady vs girl

young lady and girl both are nouns.

Word	Noun	Adjective	Verb	Adverb
young lady	Yes	No	No	No
girl	Yes	No	No	No

As nouns, young lady and girl are synonyms defined as:

Other synonyms of young lady include fille, miss, missy, young woman.

young lady (noun)	girl (noun)
a young female	a young female
	a girl or young woman with whom a man is romantically involved
	a youthful female person
	a friendly informal reference to a grown woman
	a female human offspring