Cistern is not medieval terminology. What do you call the cistern on your toilet?
People do use obscure words intentionally to create an archaic feel, or just because they think it sounds good. But that doesn't mean that's what's happening every time you learn a new word. 'Cistern' is a normal, everyday word.
For the design of published adventures, I agree. Bullet point descriptions of key features are more useful. I would never read boxed text aloud anyway.
But I wouldn't mind if the bullet points included an unfamiliar word. There are free dictionaries online.
