1. a crosspiece separating a door or the like from a window or fanlight above it.
2. Also called transom light, transom window. a window above such a crosspiece.
3. a crossbar of wood or stone, dividing a window horizontally.
4. a window so divided.
5. Nautical .
a. a flat termination to a stern, above the water line.
b. framework running athwartships in way of the sternpost of a steel or iron vessel, used as a support for the frames of the counter.
6. Artillery . a metal piece connecting the sidepieces of the tail or the cheeks of a gun carriage.