warn in WordNet English dictionary

1. 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"
   warn  discourage  admonish  monish 
   
2. 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"
   warn 
   
3. notify, usually in advance
   "I warned you that I would ask some difficult questions"
   warn 
   
4. ask to go away
   "The old man warned the children off his property"
   warn