transom
noun [ C ] uk/ˈtræn.səm/ us/ˈtræn.səm/
architecture specialized（门窗的）横档，横楣
a horizontal bar of stone or wood across a window, or separating the top of a window or door from a small window above
US (also transom window); (UK fanlight)气窗（门上方的小窗）
a small window over the top of a door