Criminal ring with sex appeal (6)
I believe the answer is:
bandit
'criminal' is the definition.
(bandit is a kind of criminal)
'ring with sex appeal' is the wordplay.
'ring' becomes 'band' ('band' can be a synonym of 'ring').
'with' means one lot of letters go next to another.
'sex appeal' becomes 'it'.
'band'+'it'='BANDIT'
(Other definitions for bandit that I've seen before include "Violent robber" , "Member of a robber gang" , "Crook" , "Marauder" , "Enemy aircraft" .)