... Sebas (Σέβας), awe or veneration, was compounded into the word Sebastos (Σεβαστός), as a translation for Augustus, the imperial title coined by Octavianus to express his own peculiar sacred majesty.
     It was not, however, apparently used for the original Augustus; at least St. Luke calls him Αὕγουστος; and its technical use probably did not begin till the division of the empire by Diocletian, and his designation of two emperors as Augusti or Sebastoi, with their heirs as Cæsars.
     Subsequently to this arrangement no one would have dared to assume the name so intimately connected with the jealous wearers of the purple; and, accordingly, it was a contemporary of the joint emperors, who is the martyr-saint of this name—Sebastianus, a soldier at Rome. (History of Christian Names, Yonge, 1884).