[syn: adult, big, full-grown, fully grown, grown, grownup]
The Collaborative International Dictionary of English v.0.48:
grownup \grownup\ adj.
   fully developed; adult; mature; -- of people and animals; as,
   Act like a grownup!.
   Syn: adult, big, full-grown, fully grown, grown.
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
grownup
    adj 1: (of animals) fully developed; "an adult animal"; "a grown
           woman" [syn: adult, big, full-grown, fully grown,
           grown, grownup]
    n 1: a fully developed person from maturity onward [syn:
         adult, grownup] [ant: juvenile, juvenile person]