A fool gives reliable information (4)
I believe the answer is:
dope
This clue might be a double definition.
'a fool' is the first definition.
(both can mean a stupid person)
'reliable information' is the second definition.
'dope' can be an answer for 'information' (dope is a kind of information). I'm not certain of the 'reliable' bit.
'gives' is the link.
Can you help me to learn more?
(Other definitions for dope that I've seen before include "Inside information (slang)" , "Drug - information" , "Illegal drugs; fool" , "cheat thereat?" , "Drugs for a dimwit" .)