APOSTOLATE, in a general sense, is used for mission. In this sense, Olearius has a discourse concerning the apostolate of Christ.
APOSTOLATE more properly denotes the dignity or office of an apostle of Christ; but it is also used, in ancient writers, for the office of a bishop. In this sense we meet with several letters, petitions, requests, &c. directed to bishops, under the title of your apostolate, or apostolatus vester. But as the title apostolatus had been appropriated to the pope, so that of apostolate became at length restrained to the sole dignity of the popedom. Every bishop's see was anciently dignified with the title of sedes apostolica, an apostolical see, which is now the peculiar denomination of the see of Rome.