enemy vs opposer

enemy and opposer both are nouns.

Word	Noun	Adjective	Verb	Adverb
enemy	Yes	No	No	No
opposer	Yes	No	No	No

As nouns, opposer is a hypernym of enemy; that is, opposer is a word with a broader meaning than enemy:

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

Other hypernyms of enemy include adversary, antagonist, opponent, resister.

enemy (noun)	opposer (noun)
an opposing military force	someone who offers opposition
any hostile group of people
an armed adversary (especially a member of an opposing military force)
a personal enemy