1. (n.) One who opposes; an adversary; an antagonist; a foe\.

2. (a.) Situated in front; opposite; hence, opposing; adverse; antagonistic.

3. (n.) One who opposes in a disputation, argument, or other verbal controversy; specifically, one who attacks some theirs or proposition, in distinction from the respondent, or defendant, who maintains it.

adversary adversative adverse alien antagonist antagonistic anti antipathetic antithetic assailant clashing combatant competitive competitor con conflicting contender contestant contradictory contrary counter counteragent cross disaccordant disputant dissentient enemy foe fractious hostile inimical match negative noncooperative obstinate opposed opposer opposing opposite oppositional oppositive oppugnant overthwart perverse recalcitrant refractory repugnant rival the opposition uncooperative unfavorable unfriendly unpropitious