Gun-wielding beast (3)
I believe the answer is:
gnu
'beast' is the definition.
(I've seen this before)
'gun-wielding' is the wordplay.
'wielding' indicates anagramming the letters (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 "Large heavy antelope" , "Large African antelope" , "Wildebeest" , "Literally wild beast" , "Strange gun for an antelope" .)