[tran.som] n [ME traunsom, transyn, prob. alter. of traversayn, fr. MF traversin, fr. traverse traverse] (15c) 1: a transverse piece in a structure: crosspiece: as a: lintel b: a horizontal crossbar in a window, over a door, or between a door and a window or fanlight above it c: the horizontal bar or member of a cross or gallows d: any of several transverse timbers or beams secured to the sternpost of a boat; also: the planking forming the stern of a square-ended boat
2: a window above a door or other window built on and commonly hinged to a transom -- over the transom : without solicitation or prior arrangement "the manuscript arrived over the transom"