antagonist

antagonist is a   Noun

Definition:

[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] 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] A medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.

Synonyms: