xakseli
Xakseli is not a standard Finnish term. The ordinary Finnish noun for an axis or axle is akseli. The form xakseli may appear as a typographical variant, a shorthand in informal writing, or as a brand or product name. It is not recognized as a separate technical term in Finnish dictionaries.
In mathematical and computing contexts, the horizontal axis of a graph is typically written as x-akseli, often
In practice, if you encounter Xakseli as a corporate name, a project title, or a user handle,
Summary: For the generic concept, use akseli; for the specific axis in graphs, use x-akseli (and y-akseli,