Source : Webster's Revised Unabridged Dictionary (1913)

Adult \A*dult"\, a. [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.

Adult \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.

Source : WordNet®

adult
     adj : (of animals) fully developed; "an adult animal"; "a grown
           woman" [syn: {big}, {full-grown}, {fully grown}, {grown},
            {grownup}]

adult
     n 1: a fully developed person from maturity onward [syn: {grownup}]
          [ant: {juvenile}]
     2: any mature animal