Meaning of warn

(verb) notify of danger, potential harm, or risk; "The director warned him that he might be fired"; "The doctor warned me about the dangers of smoking"

advise or counsel in terms of someone's behavior; "I warned him not to go too far"; "I warn you against false assumptions"; "She warned him to be quiet"

ask to go away; "The old man warned the children off his property"

notify, usually in advance; "I warned you that I would ask some difficult questions"