Sings, wasting time on song (7)
I believe the answer is:
chanson
'song' is the definition.
(I've seen this in another clue)
'sings wasting time on' is the wordplay.
I cannot really understand how this works, but
'on' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for chanson that I've seen before include "A number" , "song for Piaf?" , "(French) song" .)