Careful means paying close attention to what you're doing to avoid mistakes, damage, or danger. When you're careful carrying a glass of water across the room, you watch where you step and keep the glass steady so nothing spills. When you read test instructions carefully, you make sure you understand exactly what's being asked before you answer.

Being careful shows you understand that your actions have consequences. A careful climber checks each handhold before trusting it with her weight. A careful writer reads over his essay to catch errors before turning it in. A careful driver watches for pedestrians and follows traffic rules.

The opposite of careful is careless, which means not paying enough attention. If you're careless with your friend's borrowed book, you might leave it outside in the rain or lose it.

Sometimes people use careful as a warning: “Be careful!” means watch out for danger or pay extra attention. You can also be careful with something (like a fragile vase), careful about something (like choosing your words), or careful to do something (like being careful to lock the door).

Being careful isn't the same as being scared or slow. It means you're thinking ahead and taking the right amount of care for the situation. You'd be more careful handling your grandmother's antique teacup than your own plastic water bottle, and that makes perfect sense.