(from the Lat. abscissus, cut off), in the Cartesian system of co-ordinates, the distance of a point from the axis of y measured parallel to the horizontal axis (axis of x). Thus PS (or OR) is the abscissa of P. The word appears for the first time in a Latin work written by Stefano degli Angeli (1623-1697), a professor of mathematics in Rome. (See GEOMETRY, � Analytical.)