A fool is told off (4)
I believe the answer is:
dolt
'a fool' is the definition.
(I've seen this in another clue)
'told off' is the wordplay.
'off' is an anagram indicator.
'told' anagrammed gives 'DOLT'.
'is' is the link.
(Other definitions for dolt that I've seen before include "Slow-witted person" , "Dullard" , "dope" , "Simpleton" , "Dunce" .)