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noun. Geography. a great circle of the earth passing through the poles and any given point on the earth's surface. the half of such a circle included between the poles. Astronomy. the great circle of the celestial sphere that passes through its poles and the observer's zenith.
Also called: prime meridian. Greenwich meridian, an imaginary line, last established in 1851, that was used to indicate 0° longitude. It passes through Greenwich, a borough of London, and terminates at the North and South poles. Because it indicated 0° longitude, it was also known as the prime meridian.
meridian /mə ˈ rɪdijən/ noun. plural meridians. Britannica Dictionary definition of MERIDIAN. [count] : any one of the lines that go from the North Pole to the South Pole on maps of the world — see also prime meridian. MERIDIAN meaning: any one of the lines that go from the North Pole to the South Pole on maps of the world.
