Low-down half-wit (4)
I believe the answer is:
dope
I believe this clue is a double definition.
'low-down' is the first definition.
(synonyms)
'half-wit' is the second definition.
(I've seen this in another clue)
(Other definitions for dope that I've seen before include "Silly ass takes drugs" , "Information; nitwit" , "One simple" , "Inside information (slang)" , "Idiot; information" .)