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A prime meridian is a meridian, i.e. a line of longitude, at which the definition of longitude is zero degrees. A prime meridian and its opposite in a 360 degree-system, the 180th meridian, create a great circle. This great circle separates the sphere into two hemispheres. If one uses directions f East and West from a defined prime meridian, then they can be named Eastern and Western...
- The navel or umbilicus.
- In Greek archaeology: A central boss, as on a shield, a bowl, etc.