What does antagonist mean?
The definition of antagonist
An*tag”o*nist, n.
Etym: [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.)
A medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.

Synonyms
— Adversary; enemy; opponent; toe; competitor. See Adversary.

An*tag”o*nist, a.
Antagonistic; opposing; counteracting; as, antagonist schools of philosophy.