Window sounds a nuisance (4)
I believe the answer is:
pane
'window' is the definition.
(thesaurus)
'sounds a nuisance' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'a nuisance' becomes 'pain' (synonyms).
'pain' sounds like 'PANE'.
(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" .)