Car·te·sian a.  Of or pertaining to the French philosopher René Descartes, or his philosophy.
    The Cartesion argument for reality of matter.   --Sir W. Hamilton.
 Cartesian coordinates Geom, distance of a point from lines or planes; -- used in a system of representing geometric quantities, invented by Descartes.
 Cartesian devil, a small hollow glass figure, used in connection with a jar of water having an elastic top, to illustrate the effect of the compression or expansion of air in changing the specific gravity of bodies.
 Cartesion oval Geom., a curve such that, for any point of the curve mr + m´r´ = c, where r and r´ are the distances of the point from the two foci and m, m´ and c are constant; -- used by Descartes.