grow up verb 3exclamation 1forms 4 verb3 •To mature and become an adult.What do you want to be when you grow up?Attila grew up a nomad on the plains of Hungary •To stop acting as or like a child (often used as an imperative interjection).Will you grow up please, and stop making silly faces? •To start to develop; to flourish.Socialism grew up in the industrial cities.A town grew up at the junction of the two rivers. exclamation1 •Used to criticize childish behavior, especially that considered unreasonable for one's age.You're giggling because I said "butt"? Grow up, seriously.Grow up! The Bible is nothing more than a astrotheological allegory for things like the Sun! formsgrew up · grown up · growing up · grows up