Window section
'window section' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pane that I've seen before include "Panel of glass" , "Piece of glass in window" , "Single sheet of glass in a window" .)
(Other definitions for sill that I've seen before include "Mass of rock" , "Horizontal timber forming the bottom of a framework" , "Slab at foot of window" , "Underwater rock ledge" , "Window edge" .)