What does apostolate mean?
The definition of apostolate
A*pos”to*late, n.
Etym: [L. apostolatus, fr. apostolus. See Apostle.]

1 The dignity, office, or mission, of an apostle; apostleship. Judas had miscarried and lost his apostolate. Jer. Taylor.
2 The dignity or office of the pope, as the holder of the apostolic see.