centenarian UK /ˌsɛntəˈnɛːrɪən/US /ˌsɛnəˈnɛɹiən/adjective 2noun 1forms 3 adjective2 •Aged 100 years or more; extremely old. •Of or relating to centenarians or a centenary celebration. noun1 •One who or that which is at least 100 years old.The average age of these 203 centenarians was 102 years 5 months and 25 days. — 1894 formscentenarians · more centenarian · most centenarian