Emily Dickinson Lexicon

TRAN'SOM, n. [L. transenna, from trans, over, across.]

1. A beam or timber extended across the stern-post of a ship, to strengthen the aft-part and give it due form. Mar. Dict.
2. In architecture, the piece that is framed across a double light window; or a lintel over a door; the vane of a cross-staff. Cyc. Johnson.