I think that the difference between one word and another for the
man governing a region or a major city is administrative. Consider how comparable ranks in the different branches of the armed services or titles for comparable positions in different interior
security agencies may differ today. In
Moesia Inferior, for example, the hypatos was a legate (someone appointed) with consular rank. Hypatos
had long been used to translate Latin
consul.
From hypatos you form a verb hypateuein, to serve or hold authority in that position; hypateuontos is the present active participle in the
genitive singular of that verb; hypateuontos Longinou is a
genitive absolute. Greek, having lost the IE ablative case, uses an absolute (grammatically independent) construction in the
genitive. So it's like Longino consule, Longinus being the hypatos, when Longinus was hypatos.
That is simply what the words mean, of course.
Pat L.