in geometry, "a solid figure, all planes of which are ellipses or circles," 1721; see ellipse + -oid. From 1861 as an adjective (earlier adjective was ellipsoidal, 1831).
Entries linking to ellipsoid
ellipse n.
1753, from French ellipse (17c.), from Latin ellipsis "ellipse," also, "a falling short, deficit," from Greek elleipsis (see ellipsis). So called because the conic section of the cutting plane makes a smaller angle with the base than does the side of the cone, hence, a "falling short." The Greek word was first applied by Apollonius of Perga (3c. B.C.E.). to the curve which previously had been called the section of the acute-angled cone, but the word earlier had been technically applied to a rectangle one of whose sides coincides with a part of a given line (Euclid, VI. 27).
-oid
word-forming element meaning "like, like that of, thing like a ______," from Latinized form of Greek -oeidēs (three syllables), from eidos "form," related to idein "to see," eidenai "to know;" literally "to see" (from PIE *weid-es-, from root *weid- "to see"). The -o- is connective or a stem vowel from the previous element. Often implying an incomplete or imperfect resemblance to the thing indicated.