adversary vs opposition

adversary and opposition both are nouns.

Word	Noun	Adjective	Verb	Adverb
adversary	Yes	No	No	No
opposition	Yes	No	No	No

As nouns, opposition is a hyponym of adversary; that is, opposition is a word with a more specific, narrower meaning than adversary:

adversary: someone who offers opposition
opposition: an armed adversary (especially a member of an opposing military force)

Other hyponyms of adversary include dueler, duelist, dueller, duellist, enemy, foe, foeman, Luddite, withstander.

adversary (noun)	opposition (noun)
someone who offers opposition	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