Transom In a clock case, a transom is a transverse horizontal bar of wood that joins the sides of the case together, providing structural support for the frame. In British clock cases, transoms are used for this purpose and are typically grooved and tongued. In architecture, a transom is a transverse horizontal structural beam or bar, or a cross piece separating a door from a window above it. ‘Transom’ or ‘transom window’ are also customary American words used for the window over this light-admitting cross piece.
