adj antagonistic; opposing; counteracting; as, antagonist schools of philosophy.
2. antagonist ·noun one who contends with another, especially in combat; an adversary; an opponent.
3. antagonist ·noun a medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.
4. antagonist ·noun a muscle which acts in opposition to another; as a flexor, which bends a part, is the antagonist of an extensor, which extends it.