Tak by to bylo opravdu 'Deo' - 5.pád je dle wikipedie stejný jako první
http://en.wikipedia.org/wiki/Latin_grammar#Cases :
Vocative: case of direct address: Cornelia, go outside. This generally
looks exactly like Nominative, except in second declension masculine
nouns ending in "us" where the "us" is turned to an "e", and second declension
masculine nouns ending in "ius", where the "ius" is turned into a long "i". E.g.,
"servus" becomes "serve", and "filius" becomes "fili". The only nouns with a
distinct vocative case ending are those in the second declension and those third
declension nouns borrowed from Ancient Greek(where the final syllable is often shortened).
Jiný zdroj s tím celkem souhlasí:
http://www.hhhh.org/perseant/libellus/aides/allgre/allgre.50.html
NOTE: The vocative singular of deus does not occur in classic Latin,
but is said to have been dee; deus (like the nominative) occurs
in the Vulgate. For the genitive plural, dívum or dívom (from dívus,
divine) is often used.
takže, oslovení Bože by bylo Deu nebo Dee.
A jak to souvisí s Apage Satanas (Odstup Satane)? Holt ta latina :-)