Adjective grownup has 1 sense
  1. adult, big, full-grown, fully grown, grown, grownup - (of animals) fully developed; "an adult animal"; "a grown woman"
    Antonym: immature (indirect, via mature)
,Noun grownup has 1 sense
  1. adult, grownup - a fully developed person from maturity onward
    --1 is a kind of person, individual, someone, somebody, mortal, human, soul
    --1 has parts: adult body
    --1 has particulars:
     caregiver; catch, match; centrist, middle of the roader, moderate, moderationist; character, eccentric, type, case; conservative, conservativist; elder, senior; ex-spouse; host; important person, influential person, personage; Jack of all trades; liberal, progressive; liberal; militarist, warmonger; oldster, old person, senior citizen, golden ager; pacifist, pacificist, disarmer; patrician; pledgee; pledger; professional, professional person; sobersides; sophisticate, man of the world; stay-at-home, homebody; stoic, unemotional person; thoroughbred