quadragenarian UK /ˌkwɒdɹəd͡ʒɪˈnɛəɹɪən/US /ˌkwɑdɹəd͡ʒɪˈnɛɹiən/adjective 1noun 1forms 1 adjective1 •Of or related to fortysomethings. noun1 •Synonym of fortysomething: a person between 40 and 49 years old. formsquadragenarians