\Tran"som\, n. [Probably fr. L. transtrum a crossbeam,
transom, from trans across. Cf. {Trestle}.]
1. (Arch.) 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}.
2. (Naut.) One of the principal transverse timbers of the
   stern, bolted to the sternpost and giving shape to the
   stern structure; -- called also {transsummer}.
3. (Gun.) The piece of wood or iron connecting the cheeks of
   some gun carriages.
4. (Surg.) The vane of a cross-staff. --Chambers.
5. (Railroad) One of the crossbeams connecting the side
   frames of a truck with each other.
{Transom knees} (Shipbuilding), knees bolted to the transoms
   and after timbers.
{Transom window}. (Arch.)
   (a) A window divided horizontally by a transom or
       transoms.
   (b) A window over a door, with a transom between.