Hard diamonds cut (7)
I believe the answer is:
severed
'cut' is the definition.
('severed' can be similar in meaning to 'cut')
'hard diamonds' is the wordplay.
'hard' becomes 'severe' ('severe' can be a synonym of 'hard').
'diamonds' becomes 'd' (abbreviation in bridge say).
'severe'+'d'='SEVERED'
(Other definitions for severed that I've seen before include "Split" , "Detached" , "Deserve (anag.)" , "parted" , "Cut in two" .)