Soothing song (7)
I believe the answer is:
lullaby
'soothing song' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lullaby that I've seen before include "Soothing song for child" , "soothe" , "Sleep-inducing song" , "Gentle song to put baby to sleep" , "Song to send one to sleep" .)