verb

1. To make (someone) aware of (something impending); especially:

2. To caution or admonish (someone) against unwise or unacceptable behaviour.

   “Don't let me catch you running in the corridor again, I warn you.”

3. (chiefly with "off", "away", and similar words) To advise or order to go or stay away.

   “A sign warns trespassers off/away from the site.”