warning
Information that tells you about danger or trouble ahead.
A warning is when someone tells you about a danger or problem before it happens, giving you time to prepare or avoid trouble. When dark clouds gather and the weather service issues a tornado warning, they're alerting people to take shelter immediately. When your teacher gives you a warning about upcoming homework, she's helping you plan ahead so you won't be caught by surprise.
Warnings come in many forms. Road signs warn drivers about sharp curves or deer crossings. A rattlesnake's rattle warns other animals to stay away. Your parents might warn you about staying out too late, or a friend might warn you that a movie is really scary. Some warnings are urgent and serious, like a fire alarm, while others are gentler reminders meant to help you make better choices.
The key thing about a warning is that it arrives before the problem, not after. It's information you can actually use. A good warning gives you a chance to respond: to study harder, drive more carefully, bring an umbrella, or change your plans.