Soothing song originally loathed by a bully, surprisingly (7)
I believe the answer is:
lullaby
'soothing song' is the definition.
(I've seen this before)
'originally loathed by a bully surprisingly' is the wordplay.
'originally' indicates taking the first letters.
'by' means one lot of letters go next to another.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
The first letter of 'loathed' is 'l'.
'a'+'bully'='abully'
'abully' with letters rearranged gives 'ullaby'.
'l'+'ullaby'='LULLABY'
(Other definitions for lullaby that I've seen before include "Soothing song for baby - Brahms wrote a good one" , "Berceuse" , "composition" , "Cradle song" , "Soothing song for infants" .)