Same word as warn:

acquaint, address, admonish, advise, advocate, alert, apprise, caution, clue, clue in, counsel, cry wolf, deprecate, direct, dissuade, enjoin, exhort, fill in, forbid, forearm, forewarn, give fair warning, give the high sign, give warning, guide, hint, inform, instruct, lay it out, make aware, notify, order, post, predict, prepare, prescribe, prompt, put on guard, recommend, remind, remonstrate, reprove, signal, suggest, summon, tell, threaten, tip, tip off, urge, wise up