Compulsive thief (12)
I believe the answer is:
kleptomaniac
'compulsive thief' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for kleptomaniac that I've seen before include "Motiveless thief" , "A man to pickle (anag) - one with an urge to steal" , "Compulsive thief" , "Obsessive thief" .)