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The meaning of Jeshurun.
http://en.wikipedia.org/wiki/Jeshurun

Jeshurun in the Hebrew Bible, is a poetic name for Israel, derived from a root word meaning upright, just or straight. Jeshurun appears four times in the Hebrew Bible — three times in Deuteronomy and once in Isaiah. It can mean the people of Israel (Deut. 32:15; 33:26), the Land of Israel (Deut. 33:5;), or the Patriarch Jacob (whom an Angel renamed Israel in Genesis 32:29):

‘But Jeshurun grew fat and kicked; you grew fat, you grew thick’[1]

‘Moses commanded a law for us, a heritage of the congregation of Jacob. He was King in Jeshurun, when the leaders of the people were gathered, all the tribes of Israel together’.[2]

‘There is no one like the God of Jeshurun, who rides the heavens to help you’.[3]

‘Fear not, O Jacob My servant, and thou, Jeshurun, whom I have chosen’. (Isa. 44:2).

In the Midrash, Rabbi Berekiah in the name of Rabbi Simon interpreted Jeshurun to mean the Patriarch Israel. (Genesis Rabbah 77:1.)

The word ‘Jeshurun’ may have a relationship to the same root as the Hebrew word “upright,” “yesharim”. Numbers appears to use the word “upright,” “yesharim,” as a play on the word “Jeshurun” to refer to the people of Israel. (Num. 23:10.) Similarly, Rabbi Berekiah in the name of Rabbi Judah b. Rabbi Simon interpreted Jeshurun to mean “the noblest and best among you.” (Genesis Rabbah 77:1.)

Rabbi Aha bar Jacob told that the breastplate of the High Priest (or Kohen Gadol) contained the words “The tribes of Jeshurun,” thus supplying the otherwise missing Hebrew letter tet in the word “tribes.” (Babylonian Talmud Yoma 73b; see also Exodus Rabbah 38:9.)

In the Zohar, Rabbi Hiya explains that “Jeshurun suggests the word shur [row, side] and indicates that he [Jacob] has his rank on this side and on the other.” (Zohar 1:177b.)

In the Chassidic discourses of the Baal Shem Tov and his students, it is suggested that the word Yeshurun comes from the root “shir”, meaning song or ring, suggesting the circular nature of melodies, i.e. that Jacob’s descendants will sing mystical melodies in the coming redemption.
References

Deut 32:15
Deut 33:4-5
Deut 33:26