What is a phrase that acts like Dramatis Personae (for listing the important characters of a play) but for the important words?
I've thought of Dramatis Vocabulum, but I'm sure there's a better answer to this that I just don't have the knowledge for.
Having said that, vocabulum is a single vocable; it would at least be necessary to say Dramatis vocabula. That does in fact sound quite good. I would recommend against dramatis verba, which, like the English "the words of the play," is a bit too general.
In Middle Latin (= Medieval Latin) you also have vocabularium, which means (and is of course the root of) "vocabulary." If Middle Latin is fine, and why would it not be, I'd recommend: Dramatis vocabularium.
