An Etymological Dictionary of Astronomy and Astrophysics

Math.: In plane Cartesian coordinates, the distance of a point from the x-axis measured parallel to the y-axis. → abscissa.

Etymology (EN): Ordinate, from N.L. (linea) ordinate (applicata) “(line applied) in order;” from ordinatus “arranged.”

Etymology (PE): Ârâ, from ârâstan “to arrange, to set in order, adorn,”
Mid.Pers. ârây-, ârâstan “to arrange, adorn;” O.Pers. rās- “to be right, straight, true,” rāsta- “straight, true” (Mod.Pers. râst “straight, true”), rād- “to prepare;”
Av. rāz- “to direct, put in line, set,” razan- “order;” Gk. oregein “to stretch out;” L. regere “to lead straight, guide, rule,” p.p. rectus “right, straight;” Skt. rji- “to make straight or right, arrange, decorate;” PIE base *reg- “move in a straight line.”