Object to minute diamonds (4)
I believe the answer is:
mind
'object to' is the definition.
(I've seen this before)
'minute diamonds' is the wordplay.
'minute' becomes 'min' (abbreviation).
'diamonds' becomes 'd' (abbreviation in bridge say).
'min'+'d'='MIND'
(Other definitions for mind that I've seen before include "Take offence (at)" , "remember" , "Intelligence" , "This can be made up" , "Seat of the faculty of reason" .)