WordWeb Online

1. Someone who offers opposition
   - adversary, opponent, opposer, resister
    
2. A muscle that relaxes while another contracts
   "when bending the elbow the triceps are the antagonist"
    
3. A drug that neutralizes or counteracts the effects of another drug

Derived forms: antagonists

See also: antagonism, antagonistic

Type of: antagonistic muscle, drug, individual, mortal, person, somebody, someone, soul

Antonym: agonist, synergist

Encyclopedia: Antagonist