upside vs top side

upside and top side both are nouns.

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

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

Other synonyms of upside include top, upper side.

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