sweetheart vs dearest

sweetheart and dearest both are nouns.

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

As nouns, sweetheart and dearest are synonyms defined as:

Other synonyms of sweetheart include baby, beloved, darling, dear, dearie, deary, honey, love, sweetie.

sweetheart (noun)	dearest (noun)
a person loved by another person	a beloved person; used as terms of endearment
a very attractive or seductive looking woman
any well-liked individual
a beloved person; used as terms of endearment

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