flip side vs opposition

flip side and opposition both are nouns.

Word	Noun	Adjective	Verb	Adverb
flip side	Yes	No	No	No
opposition	Yes	No	No	No

As nouns, opposition is a hypernym of flip side; that is, opposition is a word with a broader meaning than flip side:

Other hypernyms of flip side include oppositeness.

flip side (noun)	opposition (noun)
a different aspect of something (especially the opposite aspect)	the act of hostile groups opposing each other
	the action of opposing something that you disapprove or disagree with
	a body of people united in opposing something
	an armed adversary (especially a member of an opposing military force)
	a contestant that you are matched against
	a direction opposite to another
	the relation between opposed entities