Opponent
Opponent , adjective
[Latin opponens, -entis, present participle of opponere to set or place against, to oppose; ob (see Ob-) + ponere to place. See Position.]
Situated in front; opposite; hence, opposing; adverse; antagonistic. — Pope
Opponent , noun
1.
One who opposes; an adversary; an antagonist; a foe. — Macaulay
2.
One who opposes in a disputation, argument, or other verbal controversy; specifically, one who attacks some thesis or proposition, in distinction from the respondent, or defendant, who maintains it.
How becomingly does Philopolis exercise his office, and seasonably commit the opponent with the respondent, like a long-practiced moderator!