AGONIST

noun Etymology: Late Latin ~a competitor, from Greek agōnistēs, from agōnizesthai to contend, from agōn Date: circa 1623 one that is engaged in a struggle, 2. \from ant~] a muscle that is controlled by the action of an ant~ with which it is paired, a chemical substance capable of combining with a specific receptor on a cell and initiating the same reaction or activity typically produced by the binding endogenous substance