противник, соперник, антагонист
антагонист, противодействующий агент
имя существительное антагонист; соперник; враг, противник Синоним(ы): rival, opponent
noun 1. one that contends with or opposes another; adversary, opponent 2. an agent of physiological antagonism: as a. a muscle that contracts with and limits the action of an agonist with which it is paired — called also antagonistic muscle b. a chemical that acts within the body to reduce the physiological activity of another chemical substance (as an opiate); especially one that opposes the action on the nervous system of a drug or a substance occurring naturally in the body by combining with and blocking its nervous receptor — compare agonist 2b