prime meridian

the meridian running through Greenwich, England, from which longitude east and west is reckoned.

1860–65 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
prime meridian
the 0° meridian from which the other meridians or lines of longitude are calculated, usually taken to pass through Greenwich

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
prime meridian   (prīm)  Pronunciation Key 
The meridian with a longitude of 0°, adopted officially in 1884 as a reference line from which longitude east and west are measured and as a basis for standardized time zones. It passes through Greenwich, England, the site of the Royal Greenwich Observatory, which was founded in 1675 and which closed except as a museum in 1998. The prime meridian, together with its opposite meridian having a longitude of 180°, divide the Earth roughly into the Eastern and Western Hemispheres, with those portions of the British Isles, Europe, and Africa that lie west of the prime meridian, considered for practical purposes as belonging to the Eastern Hemisphere. See illustration at time zone.
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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary

prime meridian definition

The meridian at zero degrees longitude. All longitude is measured relative to the prime meridian, which passes through Greenwich, England.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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