noun

mullion

/ˈmʌliən/ · say it: MUL·yuhn

a vertical bar dividing panes of a window

In Architecture & Design

In more detail

1. (noun) a vertical bar of stone or metal that divides the panes of a window or the panels of a door

Examples

1. The old church windows had decorative mullions separating the small panes of glass.

How to use mullion

Mullion refers specifically to the vertical structural elements dividing window panes or door panels, and is commonly used in architectural and heritage contexts. It is distinct from a transom, which runs horizontally. The term is most familiar in discussions of traditional or period buildings, though it remains standard in architectural terminology.

Common phrases

stone mullion
lead mullion
mullioned window
mullion and transom
ornamental mullion

Synonyms

muntin · glazing bar · window bar · divider

Word family

mullioned (adjective)

A common mistake

Learners often confuse mullion (vertical) with transom (horizontal), or use mullion to describe the horizontal dividing elements of windows.

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