Block heavenly centre on two sides (4)
I believe the answer is:
veto
'block' is the definition.
(to veto is to block a decision or action)
'heavenly centre on two sides' is the wordplay.
'centre' says to take the centre.
'on' is a charade indicator (letters next to each other).
'sides' suggests removing the centre (only the letters on the sides are used).
The central letters of 'heavenly' are 've'.
'two' with its centre removed is 'to'.
've'+'to'='VETO'
(Other definitions for veto that I've seen before include "Overrule, forbid" , "Cast over-riding vote" , "Vote that blocks a decision" , "Authoritative prohibition" , "Right to reject a proposal" .)