Hold back part of song (7)
I believe the answer is:
I believe this is a double definition.
'hold back' is the first definition.
(I've seen this before)
'part of song' is the second definition.
(repeated part of a song)
(Other definitions for refrain that I've seen before include "Stop - chorus" , "Stop oneself (from doing something)" , "Kindly desist - from song?" , "Don't do that - it's a song" , "The repeated lines at the end of verses" .)