Fool repeatedly at home for killer (8)
I believe the answer is:
'for killer' is the definition.
(assassin is a kind of killer)
'fool repeatedly at home' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'repeatedly' says to double the letters.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'ass' duplicated is 'assass'.
(Other definitions for assassin that I've seen before include "Bravo!" , "Murderer (of prominent figure)" , "Killer of famous person" , "butcher" , "Hired murderer" .)