<p><strong>Noun:</strong></p><ul><li>A person engaged in a contest, conflict, struggle, etc., especially the protagonist in a literary work.</li><li>A person who is torn by inner conflict.</li><li>Physiology: A contracting muscle whose action is opposed by another muscle.</li><li>Pharmacology: A chemical substance capable of activating a receptor to induce a full or partial pharmacological response.</li></ul>