<p><strong>Noun</strong></p><ul><li>Geography: a great circle of the earth passing through the poles and any given point on the earth's surface.</li><li>the half of such a circle included between the poles.</li><li>Astronomy: the great circle of the celestial sphere that passes through its poles and the observer's zenith.</li><li>a point or period of highest development, greatest prosperity, or the like.</li><li>(in acupuncture) any of the pathways in the body along which vital energy flows.</li></ul><p><strong>Adjective</strong></p><ul><li>of or relating to a meridian.</li><li>of or relating to midday or noon: the meridian hour.</li><li>of or indicating a period of greatest prosperity, splendor, success, etc.</li></ul>