Definition of ἀποστολός (apostolos) in the BDAG.
Frederick William Danker, "ἀποστολός," A Greek-English Lexicon of the New Testament and other Early Christian Literature (BDAG) (University of Chicago Press: Chicago, 2000), 122
1. of messengers without extraordinary status delegate, envoy, messenger...
2. of messengers with extraordinary status, esp. of God's messenger, envoy...
c. but predominately in the NT... of a group of highly honored believers w. a special function as God's envoys...