GI, maniac, shot sorcerer (8)
I believe the answer is:
magician
'sorcerer' is the definition.
(I know that sorcerer can be written as magician)
'gi maniac shot' is the wordplay.
'shot' indicates anagramming the letters.
'gi'+'maniac'='gimaniac'
'gimaniac' is an anagram of 'MAGICIAN'.
(Other definitions for magician that I've seen before include "Prestidigitator" , "Conjuror, wizard" , "Wizard like cartoon Mandrake" , "trickster" , "Stage conjurer or maker of legerdemain" .)