agonist: Meaning and Definition of

ag•o•nist

1. a person engaged in a contest, conflict, struggle, etc., esp. the protagonist in a literary work.
2. a person who is torn by inner conflict.
3. a contracting muscle whose action is opposed by another muscle. Cf. antagonist (def. 3).
4. a chemical substance capable of activating a receptor to induce a full or partial pharmacological response. Cf. antagonist (def. 5).