To an old soldier, brown Bess (6)
I believe the answer is:
musket
'bess' is the definition.
Both the definition and answer are singular nouns.
Maybe there's an association between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for musket that I've seen before include "Early infantry firearm" , "[DRAGON]" , "Gun used by soldiers" , "A very old rifle" , "Old type of gun" .)