Gre ‧ go ‧ ri ‧ an cal ‧ en ‧ dar /ɡrɪˌɡɔːriən ˈkæləndə $ -dər/ BrE AmE noun [singular]
[ Date: 1600-1700 ; Origin: Because it was introduced by Pope Gregory XIII ]
the system of arranging the 365 days of the year in months and giving numbers to the years from the birth of Christ, used in the West since 1582