The term Cartesian Line is a reference to the work of French philosopher and mathematician Rene Descartes. The crossword solutions for this term are AXIS (4 letters), ERGO (4 letters), RENE (4 letters), SUM (3 letters), and YAXIS (5 letters). AXIS refers to a straight line that serves as a reference point for measurement or construction, ERGO is a Latin word meaning 'THEREFORE, ' RENE is a reference to Descartes, SUM is a mathematical term meaning the total of two or more numbers, and YAXIS is a vertical AXIS in a plane coordinate system. Together, these words refer to the Cartesian Line, which is a line used in geometry and algebra that is named after Descartes.