(in a nonfiction book, monograph, etc.) a more or less detailed alphabetical listing of names, places, and topics along with the numbers of the pages on which they are mentioned or discussed, usually included in or constituting the back matter.
a sequential arrangement of material, especially in alphabetical or numerical order.
something used or serving to point out; a sign, token, or indication: a true index of his character.
something that directs attention to some fact, condition, etc.; a guiding principle.
a pointer or indicator in a scientific instrument.