Gun-wielding animal (3)
I believe the answer is:
gnu
'animal' 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 "Gun for a kind of deer" , "Strange gun for an antelope" , "Large heavy antelope" , "animals" , "Creature" .)