Told off by fool (4)
I believe the answer is:
dolt
'fool' is the definition.
(thesaurus)
'told off' is the wordplay.
'off' indicates anagramming the letters.
'told' anagrammed gives 'DOLT'.
'by' is the link.
(Other definitions for dolt that I've seen before include "Dullard" , "Slow-witted type" , "Idiot" , "Dimwit" , "Halfwit" .)