sweetie vs sweetheart

sweetie and sweetheart both are nouns.

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

As nouns, sweetie and sweetheart are synonyms defined as:

Other synonyms of sweetie include steady, truelove.

As nouns, sweetie and sweetheart are synonyms defined as:

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

sweetie (noun)	sweetheart (noun)
a person loved by another person	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

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