Mullion

Mullion, the upright division between the lights of windows, screens, &c. in Gothic architecture. Mullions are rarely met with in Norman architecture, but they become more frequent in the Early English style, and in the Decorated and Perpendicular are very common. They have sometimes small shafts attached to them, which carry the tracery of the upper part of the windows. In late domestic architecture they are usually plain. See WINDOW.