girl vs lover

girl and lover both are nouns.

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

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

Other hypernyms of girl include adult female, woman.

girl (noun)	lover (noun)
a young female	a person who loves someone or is loved by someone
a girl or young woman with whom a man is romantically involved	an ardent follower and admirer
a youthful female person	a significant other to whom you are not related by marriage
a friendly informal reference to a grown woman
a female human offspring