Church work by fashionable composer (6)
I believe the answer is:
chopin
'composer' is the definition.
(Frederic Chopin, 1810-1849)
'church work by fashionable' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'work' becomes 'op' (abbreviation for opus).
'by' means one lot of letters go next to another.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'ch'+'op'+'in'='CHOPIN'
(Other definitions for chopin that I've seen before include "Composer of "Tristesse"" , "See 10" , "his writing noted" , "Polish composer of much piano music" , "Polish pianist-composer" .)