Definitions for z-axisˈziˌæk sɪs; ˈziˌæk siz
Random House Webster's College Dictionary
z-ax•isˈziˌæk sɪs; ˈziˌæk siz(n.)(pl.)z-ax•es
(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.
Origin of z-axis:
the third axis in a 3-dimensional coordinate system
: The axis on a graph that is usually drawn as if vertical and usually shows the range of values of a variable dependent on two other variables.