Centre corruptly holding diamonds in reserve (9)
I believe the answer is:
reticence
'reserve' is the definition.
('reticence' can be a synonym of 'reserve')
'centre corruptly holding diamonds' is the wordplay.
'corruptly' indicates anagramming the letters.
'holding' is an insertion indicator.
'diamonds' becomes 'ice' (I've seen this before).
'centre' is an anagram of 'retnce'.
'retnce' placed around 'ice' is 'RETICENCE'.
'in' is the link.
(Other definitions for reticence that I've seen before include "modesty" , "'Reserve, taciturnity (9)'" , "Shyness" , "Unwillingness to talk" , "Tendency to hold back" .)