Go by quietly with donkey (4)
I believe the answer is:
pass
'go by' is the definition.
('pass' can be a synonym of 'go by')
'quietly with donkey' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'with' is a charade indicator (letters next to each other).
'donkey' becomes 'ass' (I've seen this before).
'p'+'ass'='PASS'
(Other definitions for pass that I've seen before include "Amatory advance" , "Mountain road" , "Get through exam" , "Decline to answer" , "Elapse, go by" .)