Fool with a thousand in cash (6)
I believe the answer is:
monkey
I believe this is a double definition.
'fool with' is the first definition.
(thesaurus)
'a thousand in cash' is the second definition.
(slang term for a thousand pounds)
(Other definitions for monkey that I've seen before include "Naughty child; primate" , "Chile pine (the Araucaria tree)" , "Medium-sized primate" , "PS500 (sl.)" , "Any of various long-tailed primates" .)