meridian
n. countablen. an imaginary line on a map that goes from the North Pole to the South Pole. It helps people measure how far east or west a place is.
n. an imaginary great circle on the Earth's surface passing through the North and South Poles at right angles to the equator. Used to measure longitude and determine time zones.
The Prime Meridian passes through Greenwich in London.
Navigators use the local meridian to determine the exact moment of noon when the sun reaches its highest point.
The establishment of a universal prime meridian was essential for synchronizing global maritime charts and creating a standardized system of international time zones during the nineteenth century.
Often used with the definite article when referring to a specific line of longitude.