Thief caught by castle (5)
I believe the answer is:
crook
'thief' is the definition.
(thesaurus)
'caught by castle' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'by' is a charade indicator (letters next to each other).
'castle' becomes 'rook' ('rook' can be a synonym of 'castle').
'c'+'rook'='CROOK'
(Other definitions for crook that I've seen before include "Criminal - taken in hand by bishop" , "Bend; criminal; staff" , "Well, no" , "Something kinky" , "Shepherd's staff" .)