-_nə̇st noun
( -s )
Etymology: Late Latin antagonista, from Greek antagōnistēs, from antagōnizesthai
1.
a. : one that contends with or opposes another (as in a fight, conflict, or other contest) : opponent , adversary
completely vanquishing his antagonist
b. : the principal opponent or foil of the main character in a drama or narrative
the crook was the antagonist to the detective hero
— opposed to protagonist
2. : an agent that acts in physiological opposition
contact between a tooth and its antagonist in the opposing jaw
as
a. : a muscle that contracts with and limits the action of an agonist with which it is paired
b. : a drug that opposes the action on the organism of another drug by a physiological, chemical, or competitive mechanism