Pronunciation: (an-tag'u-nist),[key] —n. 1. a person who is opposed to, struggles against, or competes with another; opponent; adversary.
2. the adversary of the hero or protagonist of a drama or other literary work: Iago is the antagonist of Othello. 3. Physiol.a muscle that acts in opposition to another. Cf. agonist (def. 3).
4. Dentistry.a tooth in one jaw that articulates during mastication or occlusion with a tooth in the opposing jaw.
5. Pharm.a drug that counteracts the effects of another drug.