Agonist

Part of speech: noun

Pronunciation: /ˈæ.ɡɘ.nɪst/

Definitions

1. A chemical that binds to a receptor and causes a response in a cell ; an individual who actively competes in a contest or struggle
2. A compound that triggers a biological receptor to produce an effect ; a participant engaging in competition or conflict
3. A molecule that stimulates a receptor to generate a biological reaction ; someone involved in rivalry or opposition in an event

Etymology: The Greek "agōnistēs" meant a competitor in the public games, a contestant who fought for a prize at festivals like the Olympics. Its root "agōn" meant a contest or struggle, and in the Greek sense the word carried the idea of combat, a fight for victory rather than a simple race. English took the Latin form "agōnista" directly, and the word's first sense was that of a combatant or champion. The modern biological sense is a far cry from the arena. In pharmacology, an agonist is a substance that binds to a receptor in the body and triggers a response, the way a key turns a lock. The image is one of opposition: the molecule contests the receptor's job and takes it up. The term's sense of rivalry and struggle survives in that metaphor, since the molecule is in effect winning a contest for the receptor.

Synonyms: protagonist, competitor, participant, champion

Antonyms: antagonist, opponent, rival