The Ancient Greek form Euphrátēs (Ancient Greek: Εὐφράτης, as if from Greek εὖ "good" and ϕράζω "I announce or declare") was adapted from Old Persian 𐎢𐎳𐎼𐎠𐎬𐎢 Ufrātu, itself from Elamite 𒌑𒅁𒊏𒌅𒅖 ú-ip-ra-tu-iš. The Elamite name is ultimately derived from a name spelt in cuneiform as 𒌓𒄒𒉣 , which read as Sumerian language is "Buranuna"" and read as Akkadian language is "Purattu"; many cuneiform signs have a Sumerian pronunciation and an Akkadian pronunciation, taken from a Sumerian word and an Akkadian word that mean the same. In Akkadian the river was called Purattu, which has been perpetuated in Semitic languages (cf. Syriac P(ə)rāṯ, Arabic al-Furrāt) and in other nearby languages of the time (cf. Hurrian Puranti, Sabarian Uruttu). The Elamite, Akkadian, and possibly Sumerian forms are suggested to be from an unrecorded substrate language. Gamkrelidze and Ivanov suggest the Proto-Sumerian *burudu "copper" (Sumerian urudu) as an origin, with an explanation that Euphrates was the river by which the copper ore was transported in rafts, since Mesopotamia was the center of copper metallurgy during the period.
The earliest references to the Euphrates come from cuneiform texts found in Shuruppak and pre-Sargonic Nippur in southern Iraq and date to the mid-3rd millennium BCE. In these texts, written in Sumerian, the Euphrates is called Buranuna (logographic: UD.KIB.NUN). The name could also be written KIB.NUN.(NA) or dKIB.NUN, with the prefix "d" indicating that the river was a divinity. In Sumerian, the name of the city of Sippar in modern-day Iraq was also written UD.KIB.NUN, indicating a historically strong relationship between the city and the river.
The Euphrates is the longest river of Western Asia. It emerges from the confluence of the Kara Su or Western Euphrates (450 kilometres (280 mi)) and the Murat Su or Eastern Euphrates (650 kilometres (400 mi)) 10 kilometres (6.2 mi) upstream from the town of Keban in southeastern Turkey. Daoudy and Frenken put the length of the Euphrates from the source of the Murat River to the confluence with the Tigris at 3,000 kilometres (1,900 mi), of which 1,230 kilometres (760 mi) is in Turkey, 710 kilometres (440 mi) in Syria and 1,060 kilometres (660 mi) in Iraq. The same figures are given by Isaev and Mikhailova. The length of the Shatt al-Arab, which connects the Euphrates and the Tigris with the Persian Gulf, is given by various sources as 145–195 kilometres (90–121 mi).
Both the Kara Su and the Murat Su rise northwest from Lake Van at elevations of 3,290 metres (10,790 ft) and 3,520 metres (11,550 ft) amsl, respectively. At the location of the Keban Dam, the two rivers, now combined into the Euphrates, have dropped to an elevation of 693 metres (2,274 ft) amsl. From Keban to the Syrian–Turkish border, the river drops another 368 metres (1,207 ft) over a distance of less than 600 kilometres (370 mi). Once the Euphrates enters the Upper Mesopotamian plains, its grade drops significantly; within Syria the river falls 163 metres (535 ft) while over the last stretch between Hīt and the Shatt al-Arab the river drops only 55 metres (180 ft).
The Euphrates receives most of its water in the form of rainfall and melting snow, resulting in peak volumes during the months April through May. Discharge in these two months accounts for 36 percent of the total annual discharge of the Euphrates, or even 60–70 percent according to one source, while low runoff occurs in summer and autumn. The average natural annual flow of the Euphrates has been determined from early- and mid-twentieth century records as 20.9 cubic kilometres (5.0 cu mi) at Keban, 36.6 cubic kilometres (8.8 cu mi) at Hīt and 21.5 cubic kilometres (5.2 cu mi) at Hindiya. However, these averages mask the high inter-annual variability in discharge; at Birecik, just north of the Syro–Turkish border, annual discharges have been measured that ranged from a low volume of 15.3 cubic kilometres (3.7 cu mi) in 1961 to a high of 42.7 cubic kilometres (10.2 cu mi) in 1963.