Convenient work left unfinished song (9)
I believe the answer is:
opportune
'convenient' is the definition.
(I've seen this before)
'work left unfinished song' is the wordplay.
'work' becomes 'op' (short for opus).
'left' becomes 'port' (left side of a ship - opposite of starboard).
'unfinished song' becomes 'une' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'op'+'port'+'une'='OPPORTUNE'
Can you help me to learn more?
(Other definitions for opportune that I've seen before include "in place" , "Timely, advantageous moment" , "Appropriate" , "Especially convenient" , "fit" .)