The definition of ἀποστολή (apostole) from A Greek-English Lexicon of the New Testament and other Early Christian Literature.
Frederick William Danker, "ἀποστολή," A Greek-English Lexicon of the New Testament and other Early Christian Literature, ed. ed, W. F. Arndt, F. W. Gingrich, and F. W. Danker (University of Chicago Press: Chicago, 2000), 121
Office of a special emissary, apostleship, office of an apostle, assignment.