Abstract? See, I completely agree (9)
I believe the answer is:
precisely
'i completely agree' is the definition.
('precisely' might be said to show agreement)
'abstract? see' is the wordplay.
'abstract?' becomes 'precis' (synonyms).
'see' becomes 'ely' (see is a place with a cathedral - e.g. Ely).
'precis'+'ely'='PRECISELY'
(Other definitions for precisely that I've seen before include "Accurately, exactly" , "without a doubt" , "Exactly, without vagueness" .)