warn

verb8

1. •
   to give someone a sign or a message that danger is near

   • We waved a flag to warn the oncoming traffic about the accident.
   • I phoned to warn him of the road closure.
2. •
   To make (someone) aware of (something impending).
3. •
   To notify or inform (someone, about something).

   • I warned him he'd be getting a huge box of birthday presents from me.
4. •
   To give warning.

   • then Iames Cephas and Iohn [...] agreed with vs that we shuld preache amonge the Hethen and they amonge the Iewes: warnynge only that we shulde remember the poore. — 1526
5. •
   To caution or admonish (someone) against unwise or unacceptable behaviour.

   • He was warned against crossing the railway tracks at night.
   • Don't let me catch you running in the corridor again, I warn you.
6. •
   To advise or order to go or stay away.

   • A sign warns trespassers off/away from the site.
7. •
   To summon (someone) to or inform of a formal meeting or duty.

   • The sheriff warned her to appear in court.
8. •
   (no longer used) To make a sound (e.g. clicking or whirring) indicating that it is about to strike or chime (an hour).

   • Hark! the clock is warning ten — 1885