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[ih-lip-soid] /ɪˈlɪp sɔɪd/
Geometry. a solid figure all plane sections of which are ellipses or circles. Typical equation: (x 2 / a 2) + (y 2 / b 2) + (z 2 / c 2) = 1.
Origin of ellipsoid
From the French word ellipsoïde, dating back to 1715-25. See ellipse, -oid Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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British Dictionary definitions for ellipsoid


  1. a geometric surface, symmetrical about the three coordinate axes, whose plane sections are ellipses or circles. Standard equation: x²/a² + y²/b² + z²/c² = 1, where ±a, ±b, ±c are the intercepts on the x-, y-, and z- axes
  2. a solid having this shape: the earth is an ellipsoid
Derived Forms
ellipsoidal (ɪlɪpˈsɔɪdəl; ˌɛl-) adjective
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
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Word Origin and History for ellipsoid

1721; see ellipse + -oid. From 1861 as an adjective (earlier adjective was ellipsoidal).

Online Etymology Dictionary, © 2010 Douglas Harper
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ellipsoid in Science
A three-dimensional geometric figure resembling a flattened sphere. Any cross section of an ellipsoid is an ellipse or circle. An ellipsoid is generated by rotating an ellipse around one of its axes.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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