Main Entry:

an·tag·o·nist

Pronunciation:

\-nist\

Function:

noun

Date:

1575

1: one that contends with or opposes another : adversary, opponent2: 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