I remember my professor from years ago providing a specific technical term for the abbreviated name tags in front of dialogue in a play, e.g.
So: The Athenians don't just call it a suit, Euthyphro, but a public indictment.
Euth: What do you mean, Socrates? Someone has indicted you, I suppose, since I certainly wouldn't condemn you of the opposite, you indicting someone else.
Another post asked a similar question, Term for the identification of the person speaking in a dialogue, but none of the answers (character name, character cue, interlocutor), seem to be the term I'm looking for. It might just be an obscure academic term that has since been simplified to character name, but if anyone can recall a different term, please let me know.