antagonist

(ăn-tăgˈə-nĭst)

1. One who opposes and contends against another; an adversary.
2. The principal character in opposition to the protagonist or hero of a narrative or drama.
3. Physiology A muscle that counteracts the action of another muscle, the agonist.
4. Biochemistry A chemical substance that interferes with the physiological action of another, especially by combining with and blocking its nerve receptor.

Related Forms:

• an·tagˌo·nisˈtic adjective

• an·tagˌo·nisˈti·cal·ly adverb