- The definition of grown-up is someone or something that is mature or intended for an adult.
An example of something that would be described as grown up is an R rated movie.
- that is an adult
- of, for, or like an adult
also written grownup
- Of, characteristic of, or intended for adults: a grown-up discussion.
- Having or showing maturity in outlook, attitude, or appearance: a grown-up attitude toward work.
(comparative more grownup, superlative most grownup)
- An adult.
(comparative more grown-up, superlative most grown-up)