The Collaborative International Dictionary of English v.0.48:

Oblongum \Ob*lon"gum\, n.; pl. Oblonga. [NL. See Oblong.]
   (Geom.)
   A prolate spheroid; a figure described by the revolution of
   an ellipse about its greater axis. Cf. Oblatum, and see
   Ellipsoid of revolution, under Ellipsoid.
   [1913 Webster]