n. - One who contends with another, especially in combat; an adversary; an opponent.
n. - A muscle which acts in opposition to another; as a flexor, which bends a part, is the antagonist of an extensor, which extends it.
n. - A medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.
a. - Antagonistic; opposing; counteracting; as, antagonist schools of philosophy.