Wickedness in current revolutionary (4)
I believe the answer is:
evil
'wickedness' is the definition.
(I know that wickedness can be written as evil)
'current revolutionary' is the wordplay.
'current' becomes 'live'.
'revolutionary' says the letters should be written backwards.
'live' backwards is 'EVIL'.
'in' is the link.
(Other definitions for evil that I've seen before include "Extremely bad" , "Extremely unpleasant" , "Malignant" , "Demonic" , "source of harm" .)