What does adult mean?
The definition of adult
A*dult”, a.
Etym: [L. adultus, p. p. of adolescere, akin to alere to nourish: cf. F. adulte. See Adolescent, Old.]

Having arrived at maturity, or to full size and strength; matured; as, an adult person or plant; an adult ape; an adult age.

A*dult”, n.
A person, animal, or plant grown to full size and strength; one who has reached maturity.

Note: In the common law, the term is applied to a person who has attained full age or legal majority; in the civil law, to males after the age of fourteen, and to females after twelve.