Desk, one found in dilapidated rectories (10)
I believe the answer is:
escritoire
'desk' is the definition.
(I've seen this before)
'one found in dilapidated rectories' is the wordplay.
'one' becomes 'i' (Roman numeral).
'found in' is an insertion indicator.
'dilapidated' is an anagram indicator.
'rectories' anagrammed gives 'escrtoire'.
'i' inserted within 'escrtoire' is 'ESCRITOIRE'.
(Other definitions for escritoire that I've seen before include "Writing desk" , "Furniture item" , "Support for author" .)