Important monk, one exercising oppressive control (3,7)
I believe the answer is:
big brother
'one exercising oppressive control' is the definition.
'important monk' is the wordplay.
'important' becomes 'big' ('big' can be similar in meaning to 'important').
'monk' becomes 'brother' (I've seen this before).
'big'+'brother'='BIG BROTHER'
(Other definitions for big brother that I've seen before include "1984's totalitarian controller -- TV reality show" , "Personification of a totalitarian state" , "Exerciser of total control over people's lives" , "oppressor, for Winston" , "dictatorial controller" .)