Definition of warn | Bee Dictionary of English

v 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
v admonish 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
v ask to go away
The old man warned the children off his property
v notify, usually in advance
I warned you that I would ask some difficult questions

PTI exclusive: Jesse Helms and Joe Biden warn that the oil firm Wintershall could face sanctions.
The Concerned Women for America, a family-values group, took it upon themselves to warn the women who fall into Jell-O-shot-induced exhibitionism and public sexuality that they'll .
Inside Al-Qaeda's Files The discovery of computer materials belonging to al-Qaeda operatives in Pakistan led American officials to warn of threats to specific facilities inside the .

Firefighters warn of charity scam
WASHINGTON D.C. -- Officials want to warn you about scammers.
June 18, 2013 - WCIA 3 Champaign-Urbana
Long Beach police warn of rental scams
Long Beach police warn of rental scams LONG BEACH >> Renters beware. Fraud Detail detectives issued a warning Tuesday that home rental scams are targeting a large number of prospective tenants, leading to the loss of their fees.
June 18, 2013 - Long Beach Press-Telegram
Officials warn of increasing fire dangers in Hualapai Mountains
Mohave County officials warn citizens on increasing fire danger levels in the Hualapai Mountains. Currently, conditions are considered “extreme.”
June 17, 2013 - Today's News-Herald

Condoleezza Rice in Khaleej Times
So I would just warn in advance not to expect that because it is really a work in progress,Rice said, adding that she expected to be back in the region in a couple of weeks ahead of the planned November peace conference.
Alistair Darling in Bloomberg
Let me assure the country and warn the banks that there will be no return to the business as usual,Darling told Labour party delegates in Brighton, southeastern England. "We will introduce legislation to end the reckless culture that puts...
Charles Schumer in International Herald Tribune
I think we are at a moment of economic crisis,Sen. Charles Schumer told Bernanke. "I am not surprised to hear experts such as your predecessor, Alan Greenspan, warn about the threat of a recession. I have begun to worry about it to."