One weapon between two officers (4)
I believe the answer is:
colt
'one weapon' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'two officers' is the wordplay.
'two officers' means two substitutions for 'officer'.
'officer' becomes 'co' (Commanding Officer abbreviation).
'officer' becomes 'lt' (abbreviation for lieutenant).
'co'+'lt'='COLT'
'between' is the link.
Can you help me to learn more?
(Other definitions for colt that I've seen before include "Young player" , "Rod" , "Young animal" , "H [HORSE]" , "Handgun -- young horse" .)