<p><strong>Adjective</strong></p><ul><li>Of or relating to the night (diurnal).</li><li>Done, occurring, or coming at night: nocturnal visit.</li><li>Active at night (diurnal): nocturnal animals.</li><li>Opening by night and closing by day, as certain flowers (diurnal).</li></ul><p><strong>Noun</strong></p><ul><li>Archaic: an astrolabe for telling time at night or for determining latitude by the position of certain stars in reference to Polaris.</li></ul>