I have a grad student as a Latin teacher. I don't feel comfortable addressing him as teacher, magister, or any other title because he doesn't really command his classroom. Rather, he guides us in interpreting the passages that we had to tell him we wanted to read at the beginning of the class. Also, he chooses to be exceptionally forgiving about missed assignments and unpreparedness.
For that reason, I want a title I can call him comfortably. I'm thinking of some sort of translation of guide, but nothing really stands out to me. "Derector" sounds like a movie producer to me, "Dux" is both too formal and too prestigious a title (considering it developed into the title of Duke), "Gubernator" would feel like I'm calling him a Republican which - while not true in a historical context - feels wrong.
"Rector" seems like a decent translation but it lacks any sense that he has authority, as far as I can tell. Maybe since he is teaching a Latin literature course (the Aeneid) he could take the title "Rector Litterarum?"
What other ways could I translate "guide," and/or what titles could confer a sense of middling dignity for a teacher?