sweetheart vs woman

sweetheart and woman both are nouns.

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

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

Other hypernyms of sweetheart include adult female.

sweetheart (noun)	woman (noun)
a person loved by another person	women as a class
a very attractive or seductive looking woman	an adult female person (as opposed to a man)
any well-liked individual	a female person who plays a significant role (wife or mistress or girlfriend) in the life of a particular man
a beloved person; used as terms of endearment

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