juvenile Pronunciation: ⁄ ˈdʒuːvənʌɪl ⁄ adjective · 1 for or relating to young people: juvenile crime · denoting a theatrical or film role representing a young person: the romantic juvenile lead · relating to young birds and animals: the prey of juvenile owlsjuvenile mortality in whelks · 2 childish; immature: she’s bored with my juvenile conversation noun · a young person. · Law a person below the age at which ordinary criminal prosecution is possible (18 in most countries): the law relating to the sentencing of juveniles · an actor playing a juvenile role. · a young bird or animal: the light-coloured plumage of ...