1. the principal character in a work of fiction • Syn: protagonist • Derivationally related forms: agony • Instance Hypernyms: fictional character, fictitious character, character • Hyponyms: antihero 2. someone involved in a contest or battle (as in an agon) • Ant: antagonist • Derivationally related forms: agonistic, agony • Hypernyms: contestant 3. a muscle that contracts while another relaxes - when bending the elbow the biceps are the agonist • Hypernyms: antagonistic muscle 4.(biochemistry) a drug that can combine with a receptor on a cell to produce a physiological reaction • Topics: biochemistry • Hypernyms: drug