verb
1.
to let one know of approaching danger or risk
police and the weather service join to warn travelers of hazardous road conditions
Synonyms: caution, forewarn
Related Word: advise, alert, apprise, inform, notify, tip; counsel, direct, guide
Idioms: address a warning to, give warning, put a flea in one's ear, put one on guard
2.
Synonyms: inform 2, acquaint, advise, apprise, clue ( or clew), fill in, notify, post, tell, wise (up)
3.
Synonyms: command , bid, charge, direct, enjoin, instruct, order, tell