upside vs upper side

upside and upper side both are nouns.

Word	Noun	Adjective	Verb	Adverb
upside	Yes	No	No	No
upper side	Yes	No	No	No

As nouns, upside and upper side are synonyms defined as:

Other synonyms of upside include top, top side.

upside (noun)	upper side (noun)
the highest or uppermost side of anything	the highest or uppermost side of anything