Window is a nuisance, we hear (4)
I believe the answer is:
pane
'window' is the definition.
(thesaurus)
'a nuisance we hear' is the wordplay.
'a nuisance' becomes 'pain' ('pain' can be a synonym of 'nuisance').
'we hear' indicates a 'sounds like' (homophone) clue.
'pain' is a homophone of 'PANE'.
'is' acts as a link.
(Other definitions for pane that I've seen before include "Single sheet of glass in a window" , "Piece of glass in window" , "Panel of glass" .)