Instrument is gong with hole in (4)
I believe the answer is:
oboe
'instrument' is the definition.
(oboe is a kind of instrument)
'gong with hole in' is the wordplay.
'gong' becomes 'obe' (I've seen this before).
'with' means one lot of letters goes inside another.
'hole in' becomes 'o' (I am not sure about the 'in' bit.**).
'obe' placed around 'o' is 'OBOE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for oboe that I've seen before include "source of notes" , "Reed instrument" , "Player" , "Slender double-reed instrument" , "Instrument used in 1d" .)