foe vs opposer

foe and opposer both are nouns.

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

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

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

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