Emily Dickinson Lexicon

AN-TAG'ON-IST, n. [Gr. αντι, against, and αγωνιστης, 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. – Campbell.
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.