Single that’s music to one’s ears (4)
I believe the answer is:
sole
'single' is the definition.
(similar in meaning)
'music to one's ears' is the wordplay.
'music' becomes 'sol' (I've seen this in another clue).
'to one's ears' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'sol'+'e'='SOLE'
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for sole that I've seen before include "Dover - -" , "Shoe part -- lone" , "A lone sort of fish - lose it" , "Flatfish; exclusive" , "Underside of footwear" .)