Window section (4)
'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" .)