The Collaborative International Dictionary of English v.0.48:

Ellipsoid \El*lip"soid\, n. [Ellipse + -oid: cf. F. ellipsoide.]
   (Geom.)
   A solid, all plane sections of which are ellipses or circles.
   See Conoid, n., 2
   (a) .
       [1913 Webster]

   Note: The ellipsoid has three principal plane sections, a, b,
         and c, each at right angles to the other two, and each
         dividing the solid into two equal and symmetrical
         parts. The lines of meeting of these principal sections
         are the axes, or principal diameters of the ellipsoid.
         The point where the three planes meet is the center.
         [1913 Webster]

   Ellipsoid of revolution, a spheroid; a solid figure
      generated by the revolution of an ellipse about one of its
      axes. It is called a prolate spheroid, or prolatum, when
      the ellipse is revolved about the major axis, and an
      oblate spheroid, or oblatum, when it is revolved about the
      minor axis. Ellipsoid

WordNet (r) 3.0 (2006):

ellipsoid of revolution
    n 1: a shape that is generated by rotating an ellipse around one
         of its axes; "it looked like a sphere but on closer
         examination I saw it was really a spheroid" [syn:
         spheroid, ellipsoid of revolution]