girl vs girlfriend

girl and girlfriend both are nouns.

Word	Noun	Adjective	Verb	Adverb
girl	Yes	No	No	No
girlfriend	Yes	No	No	No

As nouns, girl and girlfriend are synonyms defined as:

girl and girlfriend: a girl or young woman with whom a man is romantically involved

Other synonyms of girl include lady friend.

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