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.
'letter from a secluded retreat' is the wordplay.
'letter' becomes 'm'.
'from' suggests deleting specific letters.
'a secluded retreat' becomes 'hermitage' (I've seen this before).
'hermitage' with 'm' removed is 'HERITAGE'.
'in a' 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?" .)