Pronunciation: (mul'yun), [key] Archit.
1. a vertical member, as of stone or wood, between the lights of a window, the panels in wainscoting, or the like.
2. one of the radiating bars of a rose window or the like.
to furnish with, or to form into divisions by the use of, mullions.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.