Conveniences on top of cathedral? Not exactly! (7)
I believe the answer is:
loosely
'not exactly' is the definition.
(I've seen this in another clue)
'conveniences on top of cathedral?' is the wordplay.
'conveniences' becomes 'loos' (I've seen this before).
'on top of' means one lot of letters go next to another.
'cathedral?' becomes 'ely' (cathedral city in Cambridgeshire).
'loos'+'ely'='LOOSELY'
(Other definitions for loosely that I've seen before include "Not exactly" , "more or less" , "Approximately" , "Generally" , "Vaguely" .)