Describing bishop’s area, I’d upset Saint in the main (8)
I believe the answer is:
diocesan
'describing bishop's area' is the definition.
The definition suggests a singular noun which matches the answer.
'i'd upset saint in the main' is the wordplay.
'upset' says the letters should be written in reverse.
'saint' becomes 's'.
'in the' means one lot of letters goes inside another.
'main' becomes 'ocean' (synonyms).
'id' back-to-front is 'di'.
's' going within 'ocean' is 'ocesan'.
'di'+'ocesan'='DIOCESAN'
Can you help me to learn more?
(Other definitions for diocesan that I've seen before include "Of the territory of a bishop" , "Looking to see" , "Once said (anag.)" , "Of an ecclesiastical see" , "To do with bishop's territory" .)