ellipsoid

Today it means: A surface, all of whose cross sections are elliptic or circular (including the sphere), that generalises the ellipse and in Cartesian coordinates (x, y, z) is a quadric with equation x²/a² + y²/b² + z²/c² = 1. Full definition →

Ancient Greek εἶδος (eîdos) ← Proto-Hellenic *wéidos ← Proto-Indo-European *wéydos