A window divider named for "the middle" — mullions were originally structural necessities that became some of architecture's most beautiful features.
A vertical bar dividing the panes of a window, or the panels of a screen.
Alteration of Middle English monial or munnial, from Old French moienel meaning middle, from moien meaning middle, from Latin medianus meaning median Key roots: medianus (Latin: "of the middle").
Mullioned windows are the signature of Tudor and Gothic architecture, but they were originally a structural necessity, not a decorative choice. Before large panes of glass could be manufactured, windows had to be divided into small sections — the mullion held together what technology couldn't make in one piece.