British Dictionary definitions for euphrates river
a river in SW Asia, rising in E Turkey and flowing south across Syria and Iraq to join the Tigris, forming the Shatt-al-Arab, which flows to the head of the Persian Gulf: important in ancient times for the extensive irrigation of its valley (in Mesopotamia). Length: 3598 km (2235 miles)
Old English Eufrate, from Greek Euphrates, from Old Persian Ufratu, perhaps from Avestan huperethuua "good to cross over," from hu- "good" + peretu- "ford." But Kent says "probably a popular etymologizing in O.P. of a local non-Iranian name" ["Old Persian," p.176]. In Akkadian, purattu.