Master criminal aiming a carbine at head (8)
I believe the answer is:
magician
'master' is the definition.
(thesaurus)
'criminal aiming a carbine at head' is the wordplay.
'criminal' is an anagram indicator.
'head' says to take the initial letters.
The initial letters of 'carbine at' is 'ca'.
'aiming'+'ca'='aimingca'
'aimingca' with letters rearranged gives 'MAGICIAN'.
(Other definitions for magician that I've seen before include "Stage conjurer or maker of legerdemain" , "Conjuror or sorcerer" , "Sorcerer, wizard" , "Conjuror, illusionist" , "Conjuror, wizard" .)