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mullion(mŭl`yən), in architecture, a slender, upright intermediate member that subdivides an opening, as a division between panes of a window or between adjacent windows. Although the mullion occurs in some form in nearly all architectural styles, it is perhaps most characteristic of the elaborate Gothic systems of stone tracerytracery,
bands or bars of stone, wood, or other material, either subdividing an opening or standing in relief against a wall and forming an ornamental pattern of solid members and open spaces.
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A vertical bar separating two windows in a multiple window.
In folded sedimentary and metamorphic rocks, a columnar structure in which the rock columns seem to intersect.
1. a vertical member between the casements or panes of a window or the panels of a screen
2. one of the ribs on a rock face