資料來源 : Webster's Revised Unabridged Dictionary (1913)

Oval \O"val\, n.
   A body or figure in the shape of an egg, or popularly, of an
   ellipse.

   {Cassinian oval} (Geom.), the locus of a point the product of
      whose distances from two fixed points is constant; -- so
      called from Cassini, who first investigated the curve.
      Thus, in the diagram, if P moves so that P A.P B is
      constant, the point P describes a Cassinian oval. The
      locus may consist of a single closed line, as shown by the
      dotted line, or of two equal ovals about the points A and
      B.