ellipsoid vs spheroidal

ellipsoid

adj
  • Shaped like an ellipse; elliptical. 

  • Having the tridimensional shape of an ellipse rotated on its long axis. 

  • Of or pertaining to an ellipse; elliptic. 

noun
  • 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. 

  • Such a surface used as a model of the shape of the earth. 

spheroidal

adj
  • Like a spheroid; roughly spherical. 

noun
  • A spheroid 

How often have the words ellipsoid and spheroidal occurred in a corpus of books? (source: Google Ngram Viewer )