1. someone who offers opposition

    Synonyms : adversary, opponent, opposer, resister
    Antonyms : agonist
    Type Of : individual, mortal, person, somebody, someone, soul
  2. a drug that neutralizes or counteracts the effects of another drug

    Antonyms : synergist
    Type Of : drug
  3. a muscle that relaxes while another contracts

    Type Of : antagonistic muscle
    Examples :
    • when bending the elbow the triceps are the antagonist