On the Origin and Precise Definition of the Term 'Surd' So, in the course of last week's class work, I ran across the Maple function surd() that takes the real part of an nth root. However, conversation with my professor and my own research have failed to produce even an adequate definition of the term, much less a good reason for why it is used in that context in Maple.  Various dictionaries indicate that it refers to certain subsets (perhaps all of?) the irrationals, while the Wikipedia reference link uses it interchangeably with radical.  However, neither of those jive with the Maple interpretation as $\mbox{Surd}(3,x) \neq\sqrt[3]{x}\;\;\;\;\;\;\;x<0$.
So, the question is: what is a good definition for "surd"?
For bonus points, I would be fascinated to see an origin/etymology of the word as used in mathematical context.

I studied math in an Indian language, so it is easy for me to join some of the dots here. The word for hypotenuse in Sanskrit (and hence in many Indian languages) is karNa, which also means ear. When the length of a hypotenuse can be calculated easily, as when the sides are, say, 4 and 3, you get 5, it is a good hypotenuse - that is good karNa; but when the sides are, say, 4 and 4, you can only approximately get the length of the hypotenuse - that is bad karNa.
Al Khwarismi seems to have transliterated these two types into Audible numbers and Inaudible numbers, seemingly mixing numbers up with the other meaning of the word karNa, an ear. Possibly, he thought of Bad Ear = Inaudible.
The onward translation to Latin and English is clear enough. Inaudible to Deaf. I hope that makes things clear.
