Attacker and fool trouble worker (9)
I believe the answer is:
assailant
'attacker' is the definition.
(synonyms)
'fool trouble worker' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'trouble' becomes 'ail' (synonyms).
'worker' becomes 'ant' (worker is a type of ant).
'ass'+'ail'+'ant'='ASSAILANT'
'and' acts as a link.
(Other definitions for assailant that I've seen before include "One attacks" , "An attacker like mugger" , "mugger, say" , "Aggressor" , "Who would tear into" .)