dearest vs lover

dearest and lover both are nouns.

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

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

dearest (noun)	lover (noun)
a beloved person; used as terms of endearment	a person who loves someone or is loved by someone
	an ardent follower and admirer
	a significant other to whom you are not related by marriage