Antagonist, n.
Etymology: [L. antagonista, Gr. antagoniste. See Antagonism.]
1. One who contends with another, especially in combat; an adversary; an opponent. Antagonist of Heaven's Almigthy King. Milton. Our antagonists in these controversies. Hooker.
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.
3. (Med.)
2 more senses
A medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.
Syn. -- Adversary; enemy; opponent; toe; competitor. See Adversary.
1 other Webster entry under this spelling
Antagonist, a.
Antagonistic; opposing; counteracting; as, antagonist schools of philosophy.
Shades of meaning
Fernald has no entry of its own for antagonist; he lists it under enemy.
Where he writes about it:
An antagonist is one who opposes and is opposed actively and with intensity of effort; an opponent, one in whom the attitude of resistance is the more prominent; a competitor, one who seeks the same object for which another is striving; antagonists in wrestling, competitors in business, opponents in debate may contend with no personal ill will; rivals in love, ambition, etc., rarely avoid inimical feeling. — from enemy
Adversary was formerly much used in the general sense of antagonist or opponent, but is now less common, and largely restricted to the hostile sense; an adversary is ordinarily one who not only opposes another in fact, but does so with hostile spirit, or perhaps out of pure malignity; as, the great Adversary. — from enemy