1. 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. 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
3. ask to go away
- The old man warned the children off his property
4. notify, usually in advance
- I warned you that I would ask some difficult questions
Sentences with warn as a verb:
- We waved a flag to warn the oncoming traffic.
- He was warned against crossing the railway tracks at night.
- Don't let me catch you running in the corridor again, I warn you.
- I phoned to warn him of the rail strike.