The headword, presumbly extracted from the quotation given, is the aorist active participle, masculine nominative (and vocative) singular, of the verb prokaqi/hmi, I let down beforehand, deploy forward, set down before; see generally LSJ s.v.
[1] The gloss is the aorist active participle, masculine nominative (and vocative) singular, of the verb prope/mpw, I send before, ahead; see generally LSJ s.v.
[2] Quotation (transmitted, in Adler's view, via the Excerpta Constantini Porphyrogeniti) unidentifiable. A spondh/ (here in the genitive plural, spondw=n) is literally a drink-offering or libation poured in a gesture to the gods; see LSJ s.v. spondh/, OCD(4) s.v. libations, and sigma 958. It has the symbolic sense, however, of a peace-offering, treaty, peace-terms, or even a grant of safe passage; see also alpha 3649, lambda 583, epsilon 190.