Worked away quietly on a song (5)
I believe the answer is:
plied
'worked away' is the definition.
'plied' can be an answer for 'worked' (to ply is to work with a tool). I'm not certain of the 'away' bit.
'quietly on a song' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'a song' becomes 'lied' (type of German song).
'p'+'lied'='PLIED'
Can you help me to learn more?
(Other definitions for plied that I've seen before include "Regularly went" , "Worked steadily at (a trade)" , "Did regularly cross" .)