Weapon used as a tin opener by an army officer (4)
I believe the answer is:
'weapon' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'a tin opener by an army officer' is the wordplay.
'opener' says to take the initial letters.
'by' means one lot of letters go next to another.
'an army officer' becomes 'col' (short for colonel).
The initial letter of 'tin' is 't'.
't' put after 'col' is 'COLT'.
'used as' acts as a link.
Can you help me to learn more?
(Other definitions for colt that I've seen before include "Mount" , "Young Arab maybe" , "shooting with it?" , "Male horse under four years of age" , "Male pony" .)