TITLE: Derivable doesn't exist in english?
QUESTION [8 upvotes]: I have a question about terminology. See this is what happens: someone says "this function is derivable", and then another, more experienced Anglo-Saxon mathematician goes on to correct this someone, saying that the term is "differentiable". Or at least in my experience. However, in Spanish (and other romance languages I believe), the situation would be: "this function is derivable", then the more experienced, romantic-language mathematician goes "yes, but that doesn't make it differentiable". 
This is because, in Spanish, the term derivable means just that, the directional derivatives all exist, they just may not be a linear map of the direction. For example, in 1D "derivable" and "differentiable" would be the same thing (in fact this is a common stress point in lessons, how "it's not the same in higher dimensions!"). Furthermore, in 1-var. calculus I was urged to use the term "derivable", as opposed to "differentiable", so as to not gain a false understanding of the meaning of differentiability.
Call it a trifle, but I've really been wondering about this for my whole math education (and other things about real math, not to worry). So I ask if there is an analogue to "derivable" in English or if you have to work up a long phrase every time.

REPLY [2 votes]: There's another problem with using "derivable" to mean "differentiable" in English: "derive" is to "differentiate" what "give" is to "get"; the two words represent the same action from different perspectives. When a function is differentiated into it's derivative, the derivative is, in turn, derived from the original function. To say a function is derivable would be understood to mean it is a derivative (able to be derived), not that it has has one.