Gun-wielding creature (3)
I believe the answer is:
gnu
'creature' is the definition.
(type of antelope)
'gun-wielding' is the wordplay.
'wielding' indicates an anagram (I've seen 'wielded' mean this (I've seen this in other clues)).
'gun' anagrammed gives 'GNU'.
(Other definitions for gnu that I've seen before include "Wildebeest" , "Antelope sounds as if it has knowledge" , "Creature" , "animals" , "Large heavy antelope" .)