Friend retains composition for composer (10)
I believe the answer is:
palestrina
'for composer' is the definition.
(Giovanni Pierluigi da Palestrina)
'friend retains composition' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'composition' is an anagram indicator (letters arranged or composed in a different order).
'retains' anagrammed gives 'estrina'.
'pal'+'estrina'='PALESTRINA'
(Other definitions for palestrina that I've seen before include "Italian Renaissance composer" , "16th century Italian choral composer" , "He composed music" , "musician" .)