stairwell
n. B2 Upper Intermediate US //ˈstɛɹˌwɛɫ// UK //stˈeəwɛl// stair·well
n. the area inside a building where the stairs are located. It is usually a vertical space with walls around it.
n. the enclosed vertical space within a building that contains a flight of stairs.
The fire alarm went off in the stairwell.
The emergency exit is located in the stairwell on the second floor of the office building.
The architect designed the stairwell as a central atrium to allow natural light to reach the lower levels of the structure.
From stair + well.