Ass, fool (5)
I believe the answer is:
idiot
This clue is a double definition.
'ass' is the first definition.
(I've seen this before)
'fool' is the second definition.
(synonyms)
(Other definitions for idiot that I've seen before include "Fool; half-wit" , "Foolish character" , "Garret" , "Dipstick" , "Oaf" .)