fwiw Penelope, I used the Onelook reverse and entered <*ndex> to ensure capture of all variants. This nets more types of indices than you can shake a stick at, from “a index” to “zygomaticoauricular index” some 687 entries later!

Amongst them I found tab index, which seems about right to me. Not Latinate, but is it close to what you had been thinking of?

Technical description