notify of danger, potential harm, or risk
"The director warned him that he might be fired"
"The doctor warned me about the dangers of smoking"
advise or counsel in terms of someone's behavior
"I warned him not to go too far"
"I warn you against false assumptions"
"She warned him to be quiet"
To make (someone) aware of (something impending); especially:
"The captain warned the crew about the approaching storm so they could secure the cargo before it arrived."
To make (someone) aware of impending danger, evil, etc.
"The lighthouse keeper warned sailors about the hidden rocks that could sink their ships at night."
In plain English: To warn someone means to tell them something bad might happen so they can be careful.
"The teacher warned us not to run in the hallway because there might be an accident."
Usage: Use warn to tell someone about an upcoming problem or danger so they can prepare for it. Unlike advise, which suggests a course of action, this word focuses specifically on alerting others to potential risks before they occur.
A surname.
"The police chief warned that his family name was synonymous with integrity in the community."
From 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.