Instrument neighbour put up (4)
I believe the answer is:
tuba
'instrument' is the definition.
(tuba is a kind of instrument)
'neighbour put up' is the wordplay.
'neighbour' becomes 'abut' (I've seen this before).
'put up' says the letters should be written in reverse.
'abut' reversed gives 'TUBA'.
(Other definitions for tuba that I've seen before include "Deep brass instrument" , "Big brass instrument" , "Noisy instrument" , "Brass band instrument" , "Large brass wind instrument" .)