noun

1. a person sent out on a special mission
2. any of the twelve disciples sent out by Christ to teach the gospel: originally, Andrew, Bartholomew, James (the younger, son of Alphaeus), James (the elder) and John (sons of Zebedee), Jude (or Lebbaeus or Thaddaeus), Judas Iscariot, Matthew (or Levi), Philip, Simon the Canaanite, Simon (called Peter), and Thomas (or Didymus); Paul, the “Apostle to the Gentiles,” was not among the original twelve; Judas was replaced by Matthias
3. the first Christian missionary in a place
4. any of a group of early Christian missionaries
5. an early advocate or leader of a new principle or movement, esp. one aimed at reform
6. any of the twelve administrative officials of the Mormon Church

Etymology: ME < OE apostol < LL(Ec) apostolus < Gr apostolos, person sent forth < apostellein < apo-, from + stellein, to send: see still