Musical instrument’s endless beauty (4)
I believe the answer is:
bell
'musical instrument's' is the definition.
(bell is a kind of musical instrument)
'endless beauty' is the wordplay.
'endless' means to remove the last letter.
'beauty' becomes 'belle' (I've seen this before).
'belle' with its final letter taken off is 'BELL'.
(Other definitions for bell that I've seen before include "pen name" , "kind of curve" , "Ringing device" , "Buzz" , "Instrument making ringing sound" .)