meridian

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An imaginary great circle on the earth's surface passing through the North and South geographic poles.
• noun Either half of such a great circle from pole to pole. All points on the same meridian have the same longitude.
• noun Astronomy A great circle passing through the two poles of the celestial sphere and the zenith of a given observer.
• noun A curve on a surface of revolution, formed by the intersection of the surface with a plane containing the axis of revolution.
• noun A plane section of a surface of revolution containing the axis of revolution.
• noun Any of the longitudinal lines or pathways on the body along which the acupuncture points are distributed.
• noun The highest point in the sky reached by the sun or another celestial body; a zenith.
• noun The time at which the sun reaches its highest point in the sky; noon.
• noun The highest point or stage of development; peak.
• adjective Of or relating to a meridian; meridional.
• adjective Of or at midday.
• adjective Of, relating to, or constituting the highest point, as of development or power.

from The Century Dictionary.

• noun In ctenophorans, a Costa or meridional row of swimming-plates.
• noun The meridian from which the meridians bounding townships are measured.
• Of or pertaining to midday or noon; noonday: as, the meridian sun; the sun's meridian heat or splendor.
• Pertaining to the culmination or highest point or degree (the sun being highest at midday); culminating; highest before a decline: as, Athens reached its meridian glory in the age of Pericles.
• Pertaining to or marking a geographical north and south line; extending in the are of a great circle passing through the poles: as, a meridian circle on an artificial globe.
• Noting the eighth of Professor H. Rogers's twelve divisions of the Paleozoic series in the Appalachian chain of North America, the names of which suggest metaphorically the different natural periods of the day: it corresponds with the Oriskany sandstone (which see, under sandstone).
• Consummate; complete.
• noun Midday; noon.
• noun Midday repose or indulgence; nooning: used specifically as in the quotations.
• noun The highest point reached before a decline; the culmination; the point of greatest increment or development.
• noun A great circle of a sphere passing through the poles, or the half of such a circle included between the poles; in geography, such a circle drawn upon the earth; in astronomy, such a circle on the celestial sphere.
• noun Figuratively, the state or condition (in any respect) of the people of one place or region, or of persons in one sphere or plane of existence, as compared with those of or in another: as, the institutions or customs of Asia are not suited to the meridian of Europe.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Being at, or pertaining to, midday; belonging to, or passing through, the highest point attained by the sun in his diurnal course.
• adjective Pertaining to the highest point or culmination.
• noun Midday; noon.
• noun Hence: The highest point, as of success, prosperity, or the like; culmination.
• noun (Astron.) A great circle of the sphere passing through the poles of the heavens and the zenith of a given place. It is crossed by the sun at midday.
• noun (Geog.) A great circle on the surface of the earth, passing through the poles and any given place; also, the half of such a circle included between the poles.
• noun suited to the local circumstances, capabilities, or special requirements of.
• noun the meridian from which longitudes are reckoned. The meridian of Greenwich is the one commonly employed in calculations of longitude by geographers, and in actual practice, although in various countries other and different meridians, chiefly those which pass through the capitals of the countries, are occasionally used; as, in France, the meridian of Paris; in the United States, the meridian of Washington, etc.
• noun (Public Land Survey), [U.S.] a line, marked by monuments, running North and South through a section of country between other more carefully established meridians called principal meridians, used for reference in surveying.
• noun a great circle, passing through the zenith and coinciding in direction with the magnetic needle, or a line on the earth's surface having the same direction.
• noun (Astron.) an instrument consisting of a telescope attached to a large graduated circle and so mounted that the telescope revolves like the transit instrument in a meridian plane. By it the right ascension and the declination of a star may be measured in a single observation.
• noun (Astron.) any astronomical instrument having a telescope that rotates in a meridian plane.
• noun a graduated circular ring of brass, in which the artificial globe is suspended and revolves.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An imaginary great circle on the Earth's surface, passing through the geographic poles.
• noun Either half of such a great circle, all points of which have the same longitude.
• noun astronomy A great circle passing through the poles of the celestial sphere and the zenith for a particular observer.
• noun mathematics A similar line on any general surface of revolution.
• noun Any of the pathways on the body along which the vital energy is thought to flow and, therefore, the acupoints are distributed.