Is axis singular or plural?

The word axis is singular; the plural form is axes.

Axes is a Latin-derived irregular plural noun and doesn’t follow the pluralization rules of regular plural nouns. Instead of adding “-s” or “-es” to the end of the word like regular plural nouns, you change the “-is” at the end of the word to “-es” to form the plural.

You can use Scribbr’s free Grammar Checker to ensure you’re using the correct plural of axis.