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.

1715–25; < French ellipsoïde. See ellipse, -oid

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World English Dictionary
ellipsoid (ɪˈlɪpsɔɪd)
a.  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
 b.  a solid having this shape: the earth is an ellipsoid

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1721 (n.); 1861 (adj.), from ellipse + see -oid.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
ellipsoid   (ĭ-lĭp'soid')  Pronunciation Key 
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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Encyclopedia Britannica


closed surface of which all plane cross sections are either ellipses or circles. An ellipsoid is symmetrical about three mutually perpendicular axes that intersect at the centre

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The geoid height is the separation between the ellipsoid and the geoid with the surface represented as mean sea level.
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