sweetheart vs lover

sweetheart and lover both are nouns.

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

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

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

sweetheart (noun)	lover (noun)
a person loved by another person	a person who loves someone or is loved by someone
a very attractive or seductive looking woman	an ardent follower and admirer
any well-liked individual	a significant other to whom you are not related by marriage
a beloved person; used as terms of endearment

sweetheart (adjective)	lover (adjective)
privileged treatment of a favored person or corporation (sometimes unethically)