Definition of "grow up" in English

Verb

1. 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

2. To start to develop; to flourish.

   • Socialism grew up in the industrial cities.

3. To stop acting as or like a child (often used as an imperative interjection).

   • Will you grow up please, and stop making silly faces?

Interjection

1. 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!