(1):

(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.

(2):

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

(3):

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

(4):

(n.) The vane of a cross-staff.

(5):

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