Before foremost of experts, cracked codes, I see (7)
I believe the answer is:
diocese
'see' is the definition.
(thesaurus)
'before foremost of experts cracked codes i' is the wordplay.
'before' is a charade indicator (letters next to each other).
'foremost of' says to take the initial letters.
'cracked' indicates anagramming the letters.
The first letter of 'experts' is 'e'.
'codes'+'i'='codesi'
'codesi' anagrammed gives 'dioces'.
'e' after 'dioces' is 'DIOCESE'.
(Other definitions for diocese that I've seen before include "District under a bishop's jurisdiction" , "Area under bishop" , "Jurisdiction of a bishop" , "Bishop's see" , "I see cod (anag)" .)