a muscle that is restricted by the action of an antagonistic muscle with which it is paired: compare antagonist
a substance capable of combining with a receptor on the surface of a cell and initiating a reaction
[late Latin agonista competitor, from Greek agōnistēs, from agōnizesthai to contend, from agōn: see agony. Orig in the sense ‘protagonistic’; in the above senses prob back-formation from antagonist]