(~s)
Note: The spelling 'grownup' is also used. The syllable 'up' is not stressed when it is a noun.
1.
A ~ is an adult; used by or to children.
Tell children to tell a ~ if they’re being bullied.
= adult
N-COUNT
2.
Someone who is ~ is physically and mentally mature and no longer depends on their parents or another adult.
I have ~ children who’re doing well.
ADJ
3.
If you say that someone is ~, you mean that they behave in an adult way, often when they are in fact still a child.
She’s very ~.
ADJ: usu v-link ADJ
4.
Grown-up things seem suitable for or typical of adults. (INFORMAL)
Her songs tackle ~ subjects...
She talked in a ~ manner.
= adult
ADJ