a slender, vertical dividing bar between the lights of windows, doors, etc.
Origin of mullionprobably altered ; from Old French moienel ; from moien, median ; from Classical Latin medianus, middle: see mid
to furnish with or divide by mullions
A vertical member, as of stone or wood, dividing a window or other opening.
Origin of mullionAlteration of Middle English moniel, from Anglo-Norman moynel, perhaps from moienel, middle, from moien, from Latin medianus, from medius; see medhyo- in Indo-European roots.