MULLION is validvalid

to provide with vertical dividing strips [v MULLIONED, MULLIONING, MULLIONS]

45,752 of 196,601 in NWL2023·also valid in CSW24

an upright division between window panes, also MUNNION [n -S] / to provide the upright division between the panes of a window [v -ED, -ING, -S]