Complete fool loses the head (5)
I believe the answer is:
utter
'complete' is the definition.
(both can mean total)
'fool loses the head' is the wordplay.
'fool' becomes 'nutter' (both can mean an eccentric person).
'loses the head' means to remove the first letter (I've seen 'losing the head' mean this).
'nutter' with its initial letter removed is 'UTTER'.
(Other definitions for utter that I've seen before include "State - unqualified - rank" , "Give tongue to" , "Speak, express" , "Absolute - say" , "Downright" .)