Priest shot retired gypsy in organised persecution (6)
I believe the answer is:
pogrom
'persecution' is the definition.
(I know that pogrom is a type of persecution)
'priest shot retired gypsy' is the wordplay.
'priest' becomes 'p' (ecclesiastical abbreviation).
'shot' becomes 'go' (both can mean an attempt).
'retired' says the letters should be written backwards.
'gypsy' becomes 'rom' (a Rom is a member of the Roma people).
'go' reversed gives 'og'.
'p'+'og'+'rom'='POGROM'
'in organised' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for pogrom that I've seen before include "Organised persecution of an ethnic group" , "An organised massacre of a people" , "Racial massacre" , "Organised massacre of Jews" , "Mass slaughter" .)