Explanation:

- The phrase "a large bedroom for a number of people in a school or institution" refers to a room with several beds used by students or residents together.

- Creche: This is a place where babies or young children are cared for while their parents are at work. Not suitable here.

- Hostel: Usually refers to an accommodation building for students or travelers, but not specifically a large shared bedroom.

- Dormitory: A large room where several people sleep, especially in schools or institutions. This is the correct one-word substitute.

- Assembly: Means a gathering of people, not a type of room or bedroom.