Old Iynx's question today is not purely one of Latinity; the Greek tongue is involved. But I know that many here are accomplished in that language too. So: The old prayer known as the Trisagion survived in the Roman liturgy for Good Friday at least as until the days of my youth. It took the form of a curious two-part refrain in the dialog known as The Reproaches, with each part of the Trisagion sung or spoken first in Greek, and then repeated in Latin. But “Agios, o Theos” (“Holy God”) is there repeated as Sanctus Deus, though the context would seem clearly to be vocative-- I would have expected Sancte Deus. Later on, in what seems even more clearly to be a vocative context, we find “Agios Athanatos, eleison imas”. Sanctus Immortalis, miserere nobis. Surely this should be Sancte Immortalis? Now I have even less Greek than Latin. I do, however, know that the vocative of "Theos" is just "Theos" (Goodwin 195). But shouldn't the Agios (both times) and the Athanatos here end in epsilons? Is this an example of the nominative-for-vocative that Goodwin describes? If so, is the Latin just an imitation of the Greek? Thanks in advance.