\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) .
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.
{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.

\El*lip"soid\, Ellipsoidal \El`lip*soi"dal\, a.
Pertaining to, or shaped like, an ellipsoid; as, ellipsoid or
ellipsoidal form.