opponent vs withstander

opponent and withstander both are nouns.

Word	Noun	Adjective	Verb	Adverb
opponent	Yes	Yes	No	No
withstander	Yes	No	No	No

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

Other hyponyms of opponent include dueler, duelist, dueller, duellist, enemy, foe, foeman, opposition, Luddite.

opponent (noun)	withstander (noun)
someone who offers opposition	an opponent who resists with force or resolution
a contestant that you are matched against	a fighter who holds out against attack

opponent (adjective)	withstander (adjective)
characterized by active hostility