Bedtime song (7)
I believe the answer is:
lullaby
'bedtime 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" , "Cradle song" , "Go-to-sleep song" , "Soporific song" , "Gentle song to put baby to sleep" .)