transom
/ˈtrænsəm; `trænsəm/ n
1 horizontal bar of wood, stone, etc across the top of a door or window （门窗上端的）横楣, 横档. =>illus at App 1 见附录1插图, page viii.
2 (esp US) window above the transom of a door or of a larger window; fanlight （门或大窗户横楣上方的）气窗, 顶窗, 扇形窗.