Last word about section tenor delivers flat (9)
I believe the answer is:
apartment
'flat' is the definition.
('apartment' can be a synonym of 'flat')
'last word about section tenor' is the wordplay.
'last word' becomes 'amen' (I've seen this before).
'about' indicates putting letters inside.
'section' becomes 'part' ('part' can be a synonym of 'section'**).
'tenor' becomes 't'.
'amen' going around 'part' is 'apartmen'.
'apartmen'+'t'='APARTMENT'
'delivers' is the link.
(Other definitions for apartment that I've seen before include "place to live" , "Flat (chiefly US)" , "quarters" , "Suite of rooms to live in" , "Accommodation" .)