Blessing bishop with nothing on (4)
I believe the answer is:
boon
'blessing' is the definition.
(synonyms)
'bishop with nothing on' is the wordplay.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'with' means one lot of letters go next to another.
'nothing' becomes 'O' (looks like zero - 0).
'b'+'o'+'on'='BOON'
(Other definitions for boon that I've seen before include "Beneficial thing" , "Blessing - sort of companion?" , "Benefaction" , "A benefit, goes with blessing" , "Favour, request" .)