Definition: One who contends with another, especially in combat; an
adversary; an opponent.
Definition: A muscle which acts in opposition to another; as a
flexor, which bends a part, is the antagonist of an extensor, which
extends it.
Definition: A medicine which opposes the action of another medicine
or of a poison when absorbed into the blood or tissues.
Definition: Antagonistic; opposing; counteracting; as, antagonist
schools of philosophy.