B1something that makes you understand there is a possible danger or problem, especially one in the future: Completely without warning he turned up on my doorstep with all four children!There's a warning on the cigarette packet that says 'Tobacco seriously damages health'.I'm not surprised you feel ill - let it be a warning to you!Just a word of warning - restaurants in this area can be very expensive.formalThe government have today issued a warning about the dangers of sunbathing.They can't dismiss you just like that - they have to give you a written warning first.The police fired warning shots but the protesters took no notice.Threats and warningswarning sign›a physical condition that shows someone has a disease: The warning signs of the illness are respiratory problems and dizziness.Threats and warnings