Definition of antagonist
2 : an agent of physiological antagonism: such 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 (such 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 sense 2b
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Time Traveler for antagonist
The first known use of antagonist was in 1555
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