prime meridian

Noun
  1. Meridian at zero degree longitude from which east and west are reckoned (usually the Greenwich longitude in England) (synset 108616848)
    is a type of: line of longitude, meridian - an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator
    specific instances: greenwich meridian - the meridian passing through Greenwich; was internationally adopted as the earth's zero of longitude in 1884

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