Transom

n. crosspiece in a structure (across the top or middle of window, structural crosspiece in boat or bridge)

The term transom has several different meanings.
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Noun
1. a window above a door and hinged to a transom
(synonym) transom window, fanlight
(hypernym) window
2. a horizontal crosspiece across a window or separating a door from a window over it
(synonym) traverse
(hypernym) crosspiece

(n.)
The vane of a cross-staff.
  

(n.)
The piece of wood or iron connecting the cheeks of some gun carriages.
  

(n.)
One of the principal transverse timbers of the stern, bolted to the sternpost and giving shape to the stern structure; -- called also transsummer.
  

(n.)
One of the crossbeams connecting the side frames of a truck with each other.
  

(n.)
A horizontal crossbar in a window, over a door, or between a door and a window above it. Transom is the horizontal, as mullion is the vertical, bar across an opening. See Illust. of Mullion.
  

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