<p><strong>Adjective</strong></p><ul><li>Also epidemical.</li><li>(Of a disease) affecting many persons at the same time, and spreading from person to person in a locality where the disease is not permanently prevalent.</li><li>Compare pandemic.</li><li>Extremely prevalent; widespread.</li></ul><p><strong>Noun</strong></p><ul><li>A temporary prevalence of a disease.</li><li>A rapid spread or increase in the occurrence of something: an epidemic of riots.</li></ul>