Why is curvilinear used for generalized coordinate systems?

[CPW]

Hi PF.

I'm over ten years out from graduate school in physics, and I still enjoy re-reading my textbooks. I came across the word curvilinear, and thought how strange a word it is; a juxtaposition of curved and linear, which are at times understood to be opposites. The textbook was describing vector quantities (e.g. acceleration) in rectangular, plane polar, spherical, and cylindrical coordinate systems, and curvilinear was used for a generalized coordinate system.

It struck me as funny.
I'm sure it is a word used in other applications, but what?

 

[mcastillo356]

In spanish there is also the word curvilíneo, or curvilínea. Not only the contradiction you mention, but also the género question: it can be male in some cases, and female in others