agonist

ag·o·nist   (āg'ə-nĭst)    n.   One involved in a struggle or competition. Physiology A contracting muscle that is resisted or counteracted by another muscle, the antagonist. Biochemistry A drug or other chemical that can combine with a receptor on a cell to produce a physiologic reaction typical of a naturally occurring substance. [Late Latin agōnista, contender, from Greek agōnistēs, from agōn, contest; see agony.]

Main Entry: ag·o·nist
Pronunciation: 'ag-&-n&st
Function: noun
1 : a muscle that on contracting is automatically checked andcontrolled by the opposing simultaneous contraction of another muscle called also agonist muscle, prime mover; —compare ANTAGONIST a, SYNERGIST 2
2 : a chemical substance (as a drug) capable of combiningwith a receptor on a cell and initiating the same reaction or activity typically produced by the binding of an endogenous substance agonists> —compareANTAGONIST b

agonist ag·o·nist (āg'ə-nĭst)
n.

1. A contracting muscle that is resisted or counteracted by an antagonistic muscle.

2. A substance that can combine with a cell receptor to produce a reaction typical for that substance.