Lunatic (6)
I believe the answer is:
maniac
'lunatic' is the definition.
(I know that lunatic can be written as maniac)
This is all the clue.
(Other definitions for maniac that I've seen before include "Mad (keen) type" , "Obsessive enthusiast" , "Psycho" , "Can aim (anag.)" , "Extremely wild person" .)