Antagonist

n. [Fr. antagoniste, Lat. antagonista, Gr. ἀνταγωνιστής, from ἀντί, against, and ἀγωνιστής, combatant, champion, from ἀγωνίζεσθαι. See supra.]

1. One who contends with another, especially in combat; an adversary; an opponent; a competitor. “Our antagonists in these controversies.” Hooker. Antagonist of heaven’s Almighty King. Milton.
2. (Anat.) A muscle which acts in opposition to another; as a flexor, which bends a part, is the antagonist of an extensor, which extends it.

Syn.—Adversary; enemy; opponent. See ADVERSARY.