Lighten with a song, we hear (5)
I believe the answer is:
allay
'lighten' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for allay that I've seen before include "Marks of blows" , "Alleviate (hunger)" , "Lessen" , "Lay to rest (fear)" , "Assuage, ease" .)