Vertical strip between window panes (7)

I believe the answer is:

mullion

(Other definitions for mullion that I've seen before include "Vertical bar in a Gothic window" , "Vertical strip between the panes of a window" , "division between lights" , "part of window" , "Vertical bar between window panes" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.