Abrupt old Republican ringing a museum boss (7)
I believe the answer is:
curator
'museum boss' is the definition.
(I've seen this before)
'abrupt old republican ringing a' is the wordplay.
'abrupt' becomes 'curt' (I've seen this before).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'republican' becomes 'r' (abbreviation).
'ringing' is an insertion indicator.
'curt'+'o'+'r'='curtor'
'curtor' enclosing 'a' is 'CURATOR'.
(Other definitions for curator that I've seen before include "Cultural employee" , "man in the museum?" , "museum boss" , "Museum keeper" , "Custodian of a collection" .)