All new flag adopted by diocese (8)
I believe the answer is:
entirely
'all' is the definition.
(I've seen this before)
'new flag adopted by diocese' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'flag' becomes 'tire' (both can mean to become weary).
'adopted by' is an insertion indicator (I've seen this in other clues).
'diocese' becomes 'ely' (I've seen this before).
'n'+'tire'='ntire'
'ntire' inserted into 'ely' is 'ENTIRELY'.
(Other definitions for entirely that I've seen before include "Without reservation" , "Wholly and completely" , "Altogether" , "Fully or absolutely" , "without qualification _" .)