noun x- axis a reference axis, usually horizontal, of a graph or two- or three-dimensional Cartesian coordinate system along which the x-coordinate is measured 0
noun x- axis the horizontal, or more nearly horizontal, axis in a plane Cartesian coordinate system, along which the abscissa is measured 0
noun x- axis a similar axis that is perpendicular to the y-axis and the z-axis of a three-dimensional Cartesian coordinate system 0
