It comes down to use in a letter from a secluded retreat (8)
I believe the answer is:
heritage
'it comes down to use' is the definition.
The definition suggests a singular noun which matches the answer.
'a letter from a secluded retreat' is the wordplay.
'a letter' becomes 'm'.
'from' is a deletion indicator.
'a secluded retreat' becomes 'hermitage' (I've seen this before).
'hermitage' with 'm' taken away is 'HERITAGE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for heritage that I've seen before include "Objects and cultural traditions passed down" , "NT's domain" , "Received culture and background" , "Property or practices passed down" , "historical collection?" .)