upper side vs upside

upper side and upside both are nouns.

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

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

Other synonyms of upper side include top, top side.

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