Unto Shem also, the father of all the children of Eber, the brother of Japheth the elder, even to him were children born. Shem also, the father of all the children of Eber - It is generally supposed that the Hebrews derived their name from Eber or Heber, son of Shem; but it appears much more likely that they had it from the circumstance of Abraham passing over (for so the word עבר abar signifies) the river Euphrates to come into the land of Canaan. See the history of Abraham, Genesis 14:13 (note).
Related Commentaries of Genesis 10:21
Genesis 10:21
21 Unto Shem also, the father of all the children of Eber, the brother of Japheth the elder, even to him were children born.