When working in a 2D coordinate system you could say that X is the horizontal axis and Y is the vertical axis.
Extending this to 3D, is there a similar word for the Z axis?
(I'm aware of Width, Height and Depth, but obviously horizontal and vertical aren't synonymous to width and height, which is why I don't want to call the Z axis the depth axis.)
Best Answer
I doubt there is such a co-hyponym (if we can call it that) to horizontal and vertical. You'll need to use an alternative name.
If you imagine the 3 axes, then the Z would appear "on the same level" as the X one. Depending on which ones you consider, 2 of the 3 will appear as such and actually, they are.
If you look at the Wikipedia page for Cartesian Coordinate System, under the section Cartesian Space it says:
Emphasis mine. It says they are rarely used, but I doubt there are many other alternative terms, other than Z-axis, depth, and so on; they're the most appropriate terms, if you're looking for something technical.