1911 Encyclopædia Britannica/Ordinate

ORDINATE, in the Cartesian system of co-ordinates, the distance of a point from the horizontal axis (axis of x) measured parallel to the axis of y. Thus PR is the ordinate of P. The word appears to have been first used by René Descartes, and to be derived from lineae ordinatae, a term used by Roman surveyors for parallel lines. (See Geometry: Analytical.)