Detailed Definition of Shari'ah Needed

I am looking for an authentic definition of Shari'ah (based on books by traditional scholars, ancient and contemporary). I've searched half a dozen books, but no author deems it fit to explain it in more than few sentences. Authors assume that this is a self-explanatory term = Islamic Law; however, i believe a clear understanding of scope and original meaning of this term, technically, is very important in this age of confusion.