is a specific kind of: individual, mortal, person, somebody, someone, soul.

is a broader term that covers: dueler, duelist, dueller, duellist | enemy, foe, foeman, opposition | Luddite | withstander.

instances of which are: Antichrist.

is the opposite of: agonist.

derivation: antagonism | antagonism | antagonism, enmity, hostility | oppose | contradict, controvert, oppose | defend, fight, fight back, fight down, oppose | oppose, react | balk, baulk, jib, resist | opponent, opposing | antagonistic, counter.