Torment is base and wicked (7)
I believe the answer is:
bedevil
'torment' is the definition.
(I know that torment can be written as bedevil)
'base and wicked' is the wordplay.
'base' becomes 'bed' (both can mean the bottom of something).
'and' means one lot of letters go next to another.
'wicked' becomes 'evil' (associated in meaning).
'bed'+'evil'='BEDEVIL'
'is' is the link.
(Other definitions for bedevil that I've seen before include "Cause problems for" , "Afflict" , "Throw into confusion" , "Worry, harass" , "trouble" .)