Polytheists initially sacrificed their local banker (5)
I believe the answer is:
indus
'banker' is the definition.
(I've seen this before)
'polytheists initially sacrificed' is the wordplay.
'polytheists' becomes 'hindus' (Hindus believe in multiple gods).
'initially sacrificed' means to remove the first letter.
'hindus' with its first letter taken off is 'INDUS'.
'their local' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for indus that I've seen before include "Punjab river" , "9 of Pakistan" , "River flowing from Tibet to the Arabian Sea" , "Long Asian river" , "River rising in Tibet" .)