valentine vs sweetie

valentine and sweetie both are nouns.

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

As nouns, sweetie is a hypernym of valentine; that is, sweetie is a word with a broader meaning than valentine:

valentine: a sweetheart chosen to receive a greeting on Saint Valentine's Day
sweetie: a person loved by another person

Other hypernyms of valentine include steady, sweetheart, truelove.

valentine (noun)	sweetie (noun)
a sweetheart chosen to receive a greeting on Saint Valentine's Day	a person loved by another person
	a beloved person; used as terms of endearment