The verb warn has 4 senses (first 2 from tagged texts)
1. (22) warn -- (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")
2. (5) warn, discourage, admonish, monish -- (admonish 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")
3. warn -- (ask to go away; "The old man warned the children off his property")
4. warn -- (notify, usually in advance; "I warned you that I would ask some difficult questions")