HETERIARCH, HETERIARCHA, in antiquity, an officer in the Greek empire, whereof there were two species; the one called simply heteriarch, and the other great heteriarch, who had the direction of the former.
The word is Greek, ἑταῖρος, formed of the Greek ἑταῖρος focius, "companion, ally," and ἄρχω imperium, "command." Their principal function was to command the troops of the allies; besides which, they had some other duties in the emperor's court, described by Codin. De Officiis, cap. 5. n. 30, 31, 32, 37.