Definition of mullion in US English:



  • A vertical bar between the panes of glass in a window.

    Compare with transom
    • ‘There are several well dressed blocks of lime stone scattered about the graveyard, one of them being part of the cap of the ogee-headed window divided by a mullion.’
    • ‘Externally what catch the eye are the closely spaced vertical timbers (close studding), quatrefoil decoration, and windows with moulded timber mullions.’
    • ‘Vertical and horizontal extruded aluminum mullions serve as the structural members.’
    • ‘Simple details make the space special: window mullions are spaced so they don't block the view of Peter, who is tall, or Betsy, who is shorter.’
    • ‘The delicate glass facades of the south and west sides with their trussed glass mullions and oiled oak transoms are surrounded by tall, elegant and immensely thin colonnades.’
    • ‘In this work, appropriately titled Across the Street, a window with soot-black mullions gives onto a view of geometric shrubbery in the near distance, beyond which the built landscape stacks in blocks and meets the sky.’
    • ‘The configuration and mullion patterns of several of the windows also seemed to evoke Marion's hand.’
    • ‘The mullions of the interior window walls line up with those of the exterior, creating a seamless appearance.’
    • ‘The vertical mullions and stainless steel double chimney recall the pine trees that surround and almost engulf the house.’
    • ‘The family has no thought of moving, but Mrs Huyshe-Shire fears for the historic stained glass as the state of the mullions gets worse.’
    • ‘The clear glass skin of the banking and ATM hall is held in place by slim vertical mullions, emphasizing its sleek, diaphanous quality.’
    • ‘Naturalism could, however, conflict with the demands of the setting, as in the stained glass at Fairford church, where the stone mullions cut across compositions designed as a unity.’
    • ‘The pavilion's all glass structure, with its transparent mullions and ceiling joists, is perhaps no longer very radical: we have had several varieties of such transparent sheds over the last decade.’
    • ‘Unusually thin mullions span the tall space, turning it into a gigantic glass jigsaw puzzle recomposing the view.’
    • ‘The houses are mainly terraced, built in Yorkshire stone with traditional Victorian sash windows, stone mullions and slate roofs.’
    • ‘It was just possible to see them both at the same time by standing in the Garden Court and viewing the Ingres at an angle through the mullions and glass panes of a doorway, but a little back-and-forthing proved more rewarding.’
    • ‘Glass manufacturers and structural engineers are testing not only new glass interlayers, but also new window systems, including mullions, frames and anchors.’
    • ‘The views from this space are hacked up with ribbon windows that are actually thin vertical pieces of glass separated with heavy mullions that frustrate your attempts to enjoy the sweeping view.’
    • ‘Both walls have fixed glazing with custom-built mullions and transoms.’


Mid 16th century: probably an altered form of monial.