Uncertain means not knowing for sure what will happen, what is true, or what to do. When you're uncertain about an answer on a test, you're not confident it's correct. When the weather forecast says there's an uncertain chance of rain, it means people can't predict clearly whether it will rain or not.

Uncertainty is that feeling of doubt or hesitation when you lack the information you need to be confident. A basketball player might feel uncertain about whether to shoot or pass. A student might be uncertain about which instrument to choose for band class. Scientists often deal with uncertainty when studying something new, carefully noting what they know and what remains unclear.

The opposite of uncertain is certain, which means knowing something definitely and clearly. You can be certain that two plus two equals four, but uncertain about what your friend wants for her birthday. Some uncertainty is normal: nobody knows everything, and admitting uncertainty can show honesty. You can respond to uncertainty by gathering information, thinking carefully, and making the best decision you can, even when you can't be completely certain about the outcome.