A grownup is an adult, someone who has finished growing physically and is old enough to make their own decisions and take care of themselves. When you're ten, your parents, teachers, and most of the people running things around you are grownups. They're the ones with jobs, driver's licenses, and the responsibility of paying bills and making important choices.

The word captures how children see adults: as people who've reached the mysterious stage of being fully grown. You might notice that grownups can stay up as late as they want, eat dessert first if they choose, and decide where the family goes on vacation. But with all that freedom comes responsibility: grownups have to earn money, solve problems without asking for help, and take care of others who depend on them.

Sometimes people use grownup as an adjective to describe mature or sophisticated things. A fancy restaurant might seem like a grownup place. A serious conversation about money or career choices might feel like grownup talk. When you handle a difficult situation calmly and responsibly, someone might say you're acting very grownup.

The funny thing about being a grownup is that many adults will tell you they still don't feel completely grown up inside, even when they're doing all the grownup things.