[1] The headword (presumably, though not demonstrably, extracted from the quotation given) is aorist passive participle of prosti/qhmi, masculine genitive singular. In this sense the middle rather than the passive might be expected: see LSJ s.v. B.I.1-2.
[2] Quotation (transmitted, in Adler's view, via the Excerpta Constantini Porphyrogeniti) unidentifiable. de Boor suggests tentatively that the Euthymius in question, whose name appears as 'Euphemius' in mss GVM, is actually Euphemius, archbishop of Constantinople, who may also be mentioned in kappa 780.