Armour has to capture case for postie (7)
I believe the answer is:
mailbag
'case for postie' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'armour has to capture' is the wordplay.
'armour' becomes 'mail' (mail is a kind of armour).
'has' means one lot of letters go next to another.
'to capture' becomes 'bag' (both can mean to secure or acquire).
'mail'+'bag'='MAILBAG'
Can you help me to learn more?
(Other definitions for mailbag that I've seen before include "carrier" , "Sack for carrying (American) letters" , "Postal sack" , "Sent down sewer's product" , "Sack for post" .)