mullion

mullion
/ˈmʌlɪən; `mʌljən/ n
vertical (stone, wood or metal) division between two parts of a window, esp in a large old building （窗扇间的）直棂, 竖框, 中挺. =>illus at App 1 见附录1插图, page viii.

牛津英汉双解词典