Cautioned (6)
'cautioned' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for warned that I've seen before include "Cautioned about Andrew" , "Put on the alert" , "Notified in advance" , "Notified of potential danger" .)
(Other definitions for advised that I've seen before include "Warned" , "Given recommendation" , "Informed" , "Counselled" , "Did guide" .)