/ ˈædʌlt; NAmE ; əˈdʌlt/ noun , adjective
■ noun
1.
a fully grown person who is legally responsible for their actions
SYN grown-up :
Children must be accompanied by an adult.
Why can't you two act like civilized adults?
2.
a fully grown animal :
The fish return to the river as adults in order to breed.
■ adjective
1.
fully grown or developed :
preparing young people for adult life
the adult population
adult monkeys
2.
behaving in an intelligent and responsible way; typical of what is expected of an adult
SYN grown-up :
When my parents split up, it was all very adult and open.
3.
[ only before noun ] intended for adults only, because it is about sex or contains violence :
an adult movie
—see also adulthood
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WORD ORIGIN
mid 16th cent.: from Latin adultus , past participle of adolescere grow to maturity, from ad- to + alescere grow, grow up, from alere nourish.