The Oxford Thesaurus An A-Z Dictionary of Synonyms - warning n.

1) caution, admonition, advice, counsel, caveat, word (to the wise) , tip, notification, notice, threat; lesson, example: Cyril never took seriously his doctor's warning about his cholesterol level. Let that be a warning to you not to drink and drive. 2) omen, sign, signal, indication, augury, foretoken, portent, foreshadowing, forewarning, prophecy: Sailors take that kind of sky and a falling barometer as warning of a hurricane.