Express disapproval of knight giving blessing (4)
I believe the answer is:
boon
'blessing' is the definition.
('boon' can be a synonym of 'blessing')
'express disapproval of knight' is the wordplay.
'express disapproval of' becomes 'boo' (I've seen this before).
'knight' becomes 'n' (chess**).
'boo'+'n'='BOON'
'giving' is the link.
(Other definitions for boon that I've seen before include "Godsend" , "A benefit, goes with blessing" , "Blessing - sort of companion?" , "Benefit and advantage" , "Blessing, favour" .)