Definitions for x-axisˈɛksˌæk sɪs; ˈɛksˌæk siz
Random House Webster's College Dictionary
x-ax•isˈɛksˌæk sɪs; ˈɛksˌæk siz(n.)(pl.)x-ax•es
(in a plane Cartesian coordinate system) the axis, usu. horizontal, along which the abscissa is measured and from which the ordinate is measured.
(in a three-dimensional Cartesian coordinate system) the axis along which values of x are measured and at which both y and z equal zero.
Origin of x-axis:
the horizontal axis in a plane coordinate system
The axis on a graph that is usually drawn left to right and usually shows the range of values of an independent variable.