Added 9 October 2026 grownup noun Categories: PeopleRare Words noun ! Definition from WordNet 3.1, Princeton University. More about grownup at Wordnik → Where our words come from → A fully developed person from maturity onward. adjective (of animals) fully developed. an adult animal Related Words: adultfull-grownmaturebiggrowngrown-upadulthoodmanhoodprecocioustykeyoungster Back to today's word