וְשֵׁ֨ם הַנָּהָ֤ר הַשְּׁלִישִׁי֙ חִדֶּ֔קֶל ה֥וּא הַֽהֹלֵ֖ךְ קִדְמַ֣ת אַשּׁ֑וּר וְהַנָּהָ֥ר הָֽרְבִיעִ֖י ה֥וּא פְרָֽת׃
셋째 강의 이름은 힛데겔이라 앗수르 동편으로 흐르며 넷째 강은 유브라데더라
Siftei Chakhamim
It is referred to as great, etc. Rashi is answering the question: Is not the Euphrates River the smallest of them all, for in Parshas Bereishis (2:14), it is mentioned last? Rashi explains this in Parshas Lech Lecha (Bereishis 15:18).
Mizrachi
Some commentators explain: Because it is written et (a preposition indicating action upon the object,) Pithom and et Raamses," it implies that they were already in the world before the Israelites built them. As if you say that they were named Pithom and Raamses after they built them, it should have written, "And they built for Pharaoh store-cities, Pithom and Raamses..." But this is not correct. For behold, we find (Genesis 10:11), "and he built et Nineveh and et Rechoboth the city and et Kalach," the explanation of which is Nineveh and Rechoboth the city, that exist in the world now. Here too [it means], Pithom and Raamses that are now in the world; and like (Genesis 2:14), "it is the one that flows east of Assyria," today - and not in those days. Rather the correct understanding of this is...
Rashi
הנהר הגדול THE GREAT RIVER—Because it is associated with (mentioned in connection with; see Rashi on Deuteronomy 1:7) the land of Israel, Scripture calls it “great” although it is the last mentioned of the four rivers that went out of Eden — as it is said (Genesis 2:14). And the fourth river is the Euphrates”. There is a popular proverb: “A king’s servant is a king; attach yourself to a captain and people will bow down to you” (Genesis Rabbah 16:3).