A precaution is something you do ahead of time to prevent problems or danger. When you wear a helmet before riding your bike, that's a precaution against head injuries. When a teacher has students practice fire drills, that's a precaution so everyone knows what to do if there's ever a real fire.

A precautionary measure means taking action just in case. Your parents might pack extra snacks for a road trip as a precaution against getting hungry between rest stops. A scientist handling chemicals wears gloves and goggles as precautions against spills or splashes.

Precautions don't guarantee that nothing will go wrong, but they greatly reduce the chances of trouble. A ship carries lifeboats as a precaution, hoping never to need them. A basketball player stretches before a game as a precaution against pulling a muscle.

Taking precautions shows you're thinking ahead and being responsible. It's the opposite of being reckless or careless. When you check your backpack the night before school to make sure you have everything, you're taking a simple precaution that can save you from a stressful morning.