ETYM Greek elleipsis, prop., a defect, the inclination of the ellipse to the base of the cone being in defect when compared with that of the side to the base: cf. French ellipse. Related to Ellipsis.
A closed plane curve resulting from the intersection of a circular cone and a plane cutting completely through it; SYN. oval.
Curve joining all points (loci) around two fixed points (foci) such that the sum of the distances from those points is always constant. The diameter passing through the foci is the major axis, and the diameter bisecting this at right angles is the minor axis. An ellipse is one of a series of curves known as conic sections. A slice across a cone that is not made parallel to, and does not pass through, the base will produce an ellipse.