See code is broken by European (7)
I believe the answer is:
diocese
'see' is the definition.
(thesaurus)
'code is broken by european' is the wordplay.
'broken' is an anagram indicator.
'by' means one lot of letters go next to another.
'european' becomes 'e' (abbreviation e.g. EU).
'code'+'is'='codeis'
'codeis' anagrammed gives 'dioces'.
'dioces'+'e'='DIOCESE'
(Other definitions for diocese that I've seen before include "I see cod (anag)" , "Bishop's see" , "District under care of bishop" , "Church district" , "Bishop's responsibility" .)