antagonist

ANTAG'ONIST, n. [Gr. against, and a champion. See Act and Agony.]

1. One who contends with another in combat; used primarily in the Grecian games. An adversary.

2. An opponent in controversy.

3. In anatomy, a muscle which acts in opposition to another; as a flexor, which bends a part, is the antagonist of an extensor, which extends it.

ANTAG'ONIST, a. Counteracting; opposing; combating; as, an antagonist muscle.