Separate song (6)
I believe the answer is:
strain
This clue is a double definition.
'separate' is the first definition.
(I know that strain is a type of separate)
'song' is the second definition.
(I know that song can be written as strain)
(Other definitions for strain that I've seen before include "'Stress, tension (6)'" , "Noted" , "Great effort - sieve" , "Mental tension, stress" , "Trace" .)