Εὐφράτας
From LSJ
Πρόσεχε τῷ ὑποκειμένῳ ἢ τῇ ἐνεργείᾳ ἢ τῷ δόγματι ἢ τῷ σημαινομένῳ. → Look to the essence of a thing, whether it be a point of doctrine, of practice, or of interpretation.
Russian (Dvoretsky)
Εὐφράτας: ὁ Эвфрат (начальник осадных машин в армии Кира) Xen.
Greco-Persian Names
It would seem that ευ represents here the APers. u, well, Av. hu, Skt. su; posterius is connected by Justi, IF 17, Anz. 116, with *frāta, fire (Armen. hrat; unto whom the fire is gracious. Bartholomae, Wb. 1830, however, regards the posterius as a loan word.