Naughty thief's obsession (6)
I believe the answer is:
fetish
'obsession' is the definition.
(thesaurus)
'naughty thief's' is the wordplay.
'naughty' is an anagram indicator.
'thiefs' is an anagram of 'FETISH'.
(Other definitions for fetish that I've seen before include "Object worshipped by primitive people or fixation (6)" , "magical object" , "Object worshipped as having a spirit" , "Obsession" , "An abnormal object of sexual desire" .)