Rev initially gracious with peacekeepers (3)
I believe the answer is:
Here is my best explanation:
'rev' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'initially gracious with peacekeepers' is the subsidiary indication.
'initially' says to take the initial letters.
'with' is a charade indicator (letters next to each other).
'peacekeepers' becomes 'un'.
The initial letter of 'gracious' is 'g'.
(Other definitions for gun that I've seen before include "arm", "Throttle", "Shooter", "Rev up", "An offensive weapon", "Arm", "Hand weapon", "Hired killer", "Artillery piece" and "What has barrel".)