Hebrew, Perath; Assyrian, Purat (“the stream,” or “the great stream”); Persian cuneiform, Ufratush, whence Greek Euphrates (meaning “sweet water”).
The Euphrates is first mentioned in Genesis 2:14 as one of the rivers of Paradise. In the original Hebrew, it is actually named Perath. This has been translated as Euphrates. This was the name of two different rivers, one created by God in the original paradise and existing up to the time of the worldwide Flood. After the Flood, a new river was given this same name, possibly by Noah or his family.
Matthew G. Easton:
[The post-Flood river] is first mentioned in connection with the covenant which God entered into with Abraham (15:18), when he promised to his descendants the land from the river of Egypt to the river Euphrates (compare Deuteronomy 11:24; Joshua 1:4), a covenant promise afterwards fulfilled in the extended conquests of David (2 Samuel 8:2-14; 1 Chronicles 18:3; 1 Kings 4:24). This is most likely a different river given the same name as the pre-Flood river. At the time of Abraham, it was the boundary of the kingdom to the northeast. In the ancient history of Assyria, and Babylon, and Egypt many events are recorded in which mention is made of the “great river.” Just as the Nile represented in prophecy the power of Egypt, so the Euphrates represented the Assyrian power (Isaiah 8:7; Jeremiah 2:18).
It is by far the largest and most important of all the rivers of Western Asia. From its source in the Armenian mountains to the Persian Gulf, into which it empties itself, it has a course of about 1,700 miles. It has two sources, (1) the Frat or Kara-su (i.e., “the black river”), which rises 25 miles northeast of Erzeroum; and (2) the Muradchai (i.e., “the river of desire”), which rises near Ararat, on the northern slope of Ala-tagh. At Kebban Maden, 400 miles from the source of the former, and 270 from that of the latter, they meet and form the majestic stream, which is at length joined by the Tigris at Koornah, after which it is called Shat-el-Arab, which runs in a deep and broad stream for above 140 miles to the sea. It is estimated that the alluvium brought down by these rivers encroaches on the sea at the rate of about one mile in thirty years.
It is generally called in the Bible simply “the river” (Exodus 23:31), or “the great river” (Deuteronomy 1:7).