X-axis Definition

ĕksăksĭs
x-axes
noun
The horizontal, or more nearly horizontal, axis in a plane Cartesian coordinate system, along which the abscissa is measured.
Webster's New World
A similar axis that is perpendicular to the y-axis and the z-axis of a three-dimensional Cartesian coordinate system.
Webster's New World

(algebraic geometry) The axis on a graph that is usually drawn left to right and usually shows the range of values of an independent variable.

Wiktionary

Other Word Forms of X-axis

Noun

Singular:
x-axis
Plural:
x-axes