# What is the origin of the term “Differentiable”?

I was wondering today about why the word differentiable is used for describing functions that have a derivative or are differentiable.

Perhaps because originally one considered finite differences? But that seems somewhat not right, because roughly speaking a derivative measures not the difference $f(x+h)-f(x)$, but rather the ratio $(f(x+h)-f(x))/h$.

So, could people here shed light on why we use "differentiable"? Any pointers to academic / historical / etymological explanations are also welcome. Thanks!

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