Base wickedness is torment (7)
I believe the answer is:
bedevil
'torment' is the definition.
('bedevil' can be a synonym of 'torment')
'base wickedness' is the wordplay.
'base' becomes 'bed' (bed is a kind of base).
'wickedness' becomes 'evil' ('evil' can be a synonym of 'wickedness').
'bed'+'evil'='BEDEVIL'
'is' acts as a link.
(Other definitions for bedevil that I've seen before include "Torture" , "Worry, harass" , "torment" , "Throw into confusion" , "Cause continual difficulties" .)