Labels and linguistics

Index, A History of the explains how scrolls were labeled in Ancient Greece:

In order to identify a scroll without having to unroll it, a small parchment tag-- essentially a name label-- would be glued to the roll so that it stuck out, displaying the author and title of the work. It was known as a sittybos, or more commonly sillybos (whence our word syllabus, which we use to describe the contents of a course, just as a sillybos indicates the contents of a scroll).

For the Romans, the tag was an index. Which leads to this:

Meanwhile, we may quibble over whether the Latin indices or the Anglicized indexes is the correct plural in English, but at least history has not plumped for the Greek: sillyboi.