1. meridian; meridian line
Wikipedia definition
2. Meridian (geography)A meridian (or line of longitude) is an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations along it with a given longitude. The position of a point along the meridian is given by its latitude. Each meridian is perpendicular to all circles of latitude. Each is also the same size, being half of a great circle on the Earth's surface and therefore measuring 20,003.93 km (12,429.9 miles).
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