Note echoing in some music (4)
I believe the answer is:
memo
'note' is the definition.
(a memo is a short note)
'echoing in some music' is the wordplay.
'echoing' says the letters should be written in reverse (echo can mean to reflect or bounce back).
'in' says the answer is hidden in the clue.
'omem' can be found hidden inside 'some music'.
'omem' reversed gives 'MEMO'.
(Other definitions for memo that I've seen before include "Note written as a reminder" , "A brief record of events" , "In brief, a note of events" , "Written business message, in short" , "A little something to be remembered" .)