Reporter having a bit of lunch with a guerrilla leader (3)

I believe the answer is:

gun

I'm a little stuck... Click here to teach me more about this clue!

'leader' is the definition.
(I know that gun is a type of liquidator)

I cannot understand how the remainder of the clue works.

(Other definitions for gun that I've seen before include "Rev up" , "Shooter" , "An offensive weapon" , "What has barrel" , "Firearm" .)

I've seen this clue in the Evening Standard.

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