What part of speech is “vestibule”

a vestibule is a noun that means a room, hallway, or other enclosed space placed between the entrance of a building and the interior. It is a common feature of churches, government buildings, theaters, apartment buildings, and other large structures. Vestibules serve to slow the entry of people into the building, creating a buffer between the outside world and the interior.

1. As I stepped into the school vestibule, I noticed the quiet atmosphere of the hallway beyond.

2. The sculpted ceilings in the vestibule of the church made it feel like a holy abode.

3. We were stopped from entering the bank by a guard stationed at the vestibule.