Main entry: adult, grownup
Definition: a fully developed person from maturity onward
Antonyms: juvenile, juvenile person
Definition: a young person, not fully developed
Main entry: grown, grownup, full-grown, fully grown, big, adult
Definition: (of animals) fully developed
Usage: an adult animal; a grown woman
Antonyms: immature
Definition: not yet mature
Antonyms: immature
Definition: characteristic of a lack of maturity