the.com/transom window

means A small, often hinged or fixed window set above a door or another window, originally used to let light and air pass between rooms or from a hallway.

from The word comes from 'transom,' the horizontal crossbar that divides a window or sits above a door frame — itself likely descended from the Latin 'transtrum,' meaning a crossbeam or crosspiece (related to 'trans,' across). Carpenters used 'transom' for centuries to name any structural crossbar before it narrowed to mean specifically the little window perched above a doorway.