Pronunciation: (wī'ak"sis),[key] —n., —pl.y-ax•esPronunciation: (wī'ak"sēz).[key]Math. 1. Also called axis of ordinates. (in a plane Cartesian coordinate system) the axis, usually vertical, along which the ordinate is measured and from which the abscissa is measured. See diag. under ordinate. 2. (in a three-dimensional Cartesian coordinate system) the axis along which values of y are measured and at which both x and z equal zero.