• synonyms


  1. an imaginary surface that coincides with mean sea level in the ocean and its extension through the continents.
  2. the geometric figure formed by this surface, an ellipsoid flattened at the poles.
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Origin of geoid

First recorded in 1880–85, geoid is from the Greek word geoeidḗs earthlike. See geo-, -oid
Related formsge·oi·dal, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for geoid

Historical Examples of geoid

British Dictionary definitions for geoid


  1. a hypothetical surface that corresponds to mean sea level and extends at the same level under the continents
  2. the shape of the earth
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

geoid in Science


  1. The hypothetical surface of the Earth that coincides everywhere with mean sea level and is perpendicular, at every point, to the direction of gravity. The geoid is used as a reference surface for astronomical measurements and for the accurate measurement of elevations on the Earth's surface.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.