agonist has 1 distinct synonym spread across 1 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is antagonist.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the principal character in a work of fiction
someone involved in a contest or battle (as in an agon)
Synonyms, antonyms and the broader and narrower relations for agonist come from Princeton University’s WordNet. Full sources and licences.
a muscle that contracts while another relaxes
“when bending the elbow the biceps are the agonist”
(biochemistry) a drug that can combine with a receptor on a cell to produce a physiological reaction