Antagonism :: Antagonism (n.) Opposition of action; counteraction or contrariety of things or principles.
Antagonist :: Antagonist (n.) One who contends with another, especially in combat; an adversary; an opponent..
Antagonist :: Antagonist (n.) A muscle which acts in opposition to another; as a flexor, which bends a part, is the antagonist of an extensor, which extends it..
Antagonist :: Antagonist (n.) A medicine which opposes the action of another medicine or of a poison when absorbed into the blood or tissues.