Pronunciation: (zē'ak"sis), [key]
—pl. z-ax•esPronunciation: (zē'ak"sēz). [key] Math.
(in a three-dimensional Cartesian coordinate system) the axis along which values of z are measured and at which both x and y equal zero.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.