Authentic quality of minister, one attached to Exeter? (10)
I believe the answer is:
canonicity
'authentic quality' is the definition.
(quality of being authentic or official)
'minister one attached to exeter?' is the wordplay.
'minister' becomes 'canon' (canon is a type of church minister).
'one' becomes 'I' (Roman numeral).
'attached to' means one lot of letters go next to another.
'exeter?' becomes 'city' (Exeter is a city).
'canon'+'i'+'city'='CANONICITY'
'of' acts as a link.
(Another definition for canonicity that I've seen is " demonstrates quality of biblical books".)