Friend in religious group names composer (8)
I believe the answer is:
schumann
'composer' is the definition.
(I know that Schumann is a composer)
'friend in religious group names' is the wordplay.
'friend' becomes 'chum' (chum is a kind of friend).
'in' indicates putting letters inside.
'religious group' becomes 'SA' (abbreviation for Salvation Army).
'names' becomes 'nn' (an abbreviation for name twice).
'chum' put inside 'sa' is 'schuma'.
'schuma'+'nn'='SCHUMANN'
(Other definitions for schumann that I've seen before include "Robert -, nineteenth century German composer" , "Nan, chums go for this composer" , "German composer, 1810-56" , "Oddly, the German composer is Nan's chum" , "German barman" .)