Total fool (5)
I believe the answer is:
'total fool' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for idiot that I've seen before include "Unwise person" , "'The -----'. novel by Dostoyevsky (1868)" , "Fool, silly person" , "Clot" , "The - (Dostoievsky)" .)