definition of
antagonist

[1] #1 antagonist n. [adversary, opponent, opposer, resister] someone who offers opposition. wn

[2] #2 antagonist n. a muscle that relaxes while another contracts; "when bending the elbow the triceps are the antagonist". wn

[3] #3 antagonist n. a drug that neutralizes or counteracts the effects of another drug. wn