<p><strong>Noun</strong></p><ul><li>Anatomy.</li><li>A large, triangular muscle covering the joint of the shoulder, the action of which raises the arm away from the side of the body.</li></ul><p><strong>Adjective</strong></p><ul><li>Anatomy.</li><li>Pertaining to or involving the deltoid.</li><li>Also in the shape of a Greek capital delta (Δ); triangular.</li></ul>