The headword is a present participle of the rare verb parabrabeu/w, here in either the masculine accusative singular or the neuter nominative/accusative plural; the former if, as is reasonable to suppose, it is extracted from the quotation given.
On this verb, attested from Polybius onwards, see generally LSJ s.v.: web address 1.
[1] Theophylact Simocatta, Histories 2.8.10, here abridged; quoted more fully at phi 91.