Minister is former old Republican (6)
I believe the answer is:
pastor
'minister' is the definition.
('pastor' can be a synonym of 'minister')
'former old republican' is the wordplay.
'former' becomes 'past' ('past' can be similar in meaning to 'former').
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'republican' becomes 'r' (abbreviation).
'past'+'o'+'r'='PASTOR'
'is' is the link.
(Other definitions for pastor that I've seen before include "Christian minister" , "Minister of religion" , "Member of the clergy" , "Old shepherd" , "who may provide a service" .)