Gregorian (adj.) Look up Gregorian at
"pertaining to Gregory," from Late Latin Gregorianus, from Gregorius (see Gregory). From c. 1600 of church music, in reference to Gregory I the Great (pope from 590-604), who traditionally codified it; 1640s in reference to new calendar (introduced 1582) from Pope Gregory XIII (1572-1585); due to Protestant resistance, the calendar was not introduced in England and the American colonies until 1752.