Instrument taken back for neighbour (4)
I believe the answer is:
abut
'neighbour' is the definition.
(I've seen this before)
'instrument taken back' is the wordplay.
'instrument' becomes 'tuba' (tuba is a kind of instrument).
'taken back' is a reversal indicator.
'tuba' reversed gives 'ABUT'.
'for' is the link.
(Other definitions for abut that I've seen before include "Tuba (anag)" , "Lean against the odd tuba" , "Lie adjacent to" , "Impinge" , "Join" .)