Neighbour coming round for instrument (4)
I believe the answer is:
tuba
'instrument' is the definition.
(tuba is a kind of instrument)
'neighbour coming round' is the wordplay.
'neighbour' becomes 'abut' (I've seen this before).
'coming round' is a reversal indicator.
'abut' written backwards gives 'TUBA'.
'for' acts as a link.
(Other definitions for tuba that I've seen before include "horn" , "member of band" , "Stop" , "part of 14 [ORCHESTRA] ?" , "music-maker" .)