ellipsoidThe equation for an ellipsoid is x2/a2 + y2/b2 + z2/c2 = 1.el·lip·soid (?-l?p?soid?)n. A geometric surface, all of whose plane sections are either ellipses or circles.el·lip?soid?, el·lip?soi?dal (?-l?p?soid?l, ?l??p-, ??l?p-) adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.el?lip?soi?dal (? l?p?s??d l, ??l ?p-, ?i l?p-) adj. pertaining to or having the form of an ellipsoid. [1825?35] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.