Meaning

verb notify of danger, potential harm, or risk

verb admonish or counsel in terms of someone's behavior

verb ask to go away

originFrom Middle English warnen, warnien (“to warn; admonish”), from Old English warnian (“to take heed; warn”), from Proto-Germanic *warnōną (“to warn; take heed”), from Proto-Indo-European *wer- (“to be aware; give heed”). Cognate with Dutch waarnen (obsolete), German Low German warnen, German warnen, Swedish varna, Icelandic varna.

Etymology from Wiktionary, CC BY-SA 3.0