Gregorian /ɡɹɪˈɡɔːɹi.ən/adjective 3noun 1forms 1 adjective3 •Of or relating to a person named Gregory, especially any of the popes of that name. •Of or pertaining to the Gregorian calendar.An average Gregorian year is 365.2425 days. •Of or relating to James Gregory (mathematician), inventor of the Gregorian telescope. noun1 •A member of the Brotherhood of Saint Gregory. formsGregorians