Song composed by Edna Rees (8)
I believe the answer is:
serenade
'song' is the definition.
(I know that serenade is a type of song)
'composed by edna rees' is the wordplay.
'composed by' is an anagram indicator (I've seen this in other clues).
'edna'+'rees'='ednarees'
'ednarees' with letters rearranged gives 'SERENADE'.
(Other definitions for serenade that I've seen before include "Evening love song" , "Music appropriate for evening" , "Noted performance" , "It's played or sung at a lover's window" , "Lover's song" .)