Two officers, one gun (4)
I believe the answer is:
colt
'one gun' is the definition.
(I've seen this before)
'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'
(Other definitions for colt that I've seen before include "Young animal" , "Youngster" , "Male horse under four years of age" , "shooting with it?" , "Young male horse or cowboy revolver" .)