Pronunciation: (ag'u-nist),[key] —n. 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. Physiol.a contracting muscle whose action is opposed by another muscle. Cf. antagonist (def. 3).
4. Pharm.a chemical substance capable of activating a receptor to induce a full or partial pharmacological response. Cf. antagonist (def. 5).