mullion
noun
mul·lion ˈməl-yən 
: a slender vertical member that forms a division between units of a window, door, or screen or is used decoratively
mullion transitive verb
Example Sentences
Recent Examples on the Web Architectural details include eyebrow dormer windows, two-story columns and spiderweb mullion windows, according to Ms. Seery. 
Sarah Paynter, WSJ, 10 Mar. 2022 Then, spread glue in the back rail mortises and on the mullion tenons. Darren Orf, Popular Mechanics, 8 Aug. 2020 Mark the locations of the mullion mortises in the back rails and rout them with a 3/8-in. Darren Orf, Popular Mechanics, 8 Aug. 2020 Mies made the mullions in the same I-beam shape as the steel structure inside the building. Michael Kimmelman, New York Times, 29 Apr. 2020 Nonetheless, Hancock’s board, determined to avoid future embarrassments, decided that as the building was repaired, each large sheet of glass should be replaced by three smaller panels, separated by mullions. Fred A. Bernstein, New York Times, 4 Mar. 2020 The paneled wood walls and lack of trim are modern touches, as is the floor-to-ceiling window, but the small panes and mullions are traditional. Mimi Read, House Beautiful, 2 Jan. 2013 Black window mullions and door and chair frames add graphic punch in a family vacation home on Sullivan's Island, South Carolina. Sarah Yang, House Beautiful, 2 June 2014 There are a variety of code violations with the most costly being a mullion that needs to be replaced on a door. Evan Frank, Milwaukee Journal Sentinel, 25 June 2018 See More
Sarah Paynter, WSJ, 10 Mar. 2022 Then, spread glue in the back rail mortises and on the mullion tenons. Darren Orf, Popular Mechanics, 8 Aug. 2020 Mark the locations of the mullion mortises in the back rails and rout them with a 3/8-in. Darren Orf, Popular Mechanics, 8 Aug. 2020 Mies made the mullions in the same I-beam shape as the steel structure inside the building. Michael Kimmelman, New York Times, 29 Apr. 2020 Nonetheless, Hancock’s board, determined to avoid future embarrassments, decided that as the building was repaired, each large sheet of glass should be replaced by three smaller panels, separated by mullions. Fred A. Bernstein, New York Times, 4 Mar. 2020 The paneled wood walls and lack of trim are modern touches, as is the floor-to-ceiling window, but the small panes and mullions are traditional. Mimi Read, House Beautiful, 2 Jan. 2013 Black window mullions and door and chair frames add graphic punch in a family vacation home on Sullivan's Island, South Carolina. Sarah Yang, House Beautiful, 2 June 2014 There are a variety of code violations with the most costly being a mullion that needs to be replaced on a door. Evan Frank, Milwaukee Journal Sentinel, 25 June 2018 See More Word History
Etymology
probably alteration of monial mullion
First Known Use
1567, in the meaning defined above