Horizontal axis is a term widely used in various fields such as mathematics, engineering, and science. However, there are several synonyms for this word. The first one is the x-axis, which is mostly used in mathematics and geometry. Another synonym is the abscissa, which is a term used in coordinate systems and graphing. A third synonym for horizontal axis is the baseline, which is commonly used in typography and graphic design. In addition, the term horizon line can also be used to describe the horizontal axis, particularly in the field of art. Lastly, the term ground plane can be used in architecture and engineering to refer to the horizontal plane on which a structure is built.