(supremely happy ), and once by mistake in Authorized Version JESURUN,
(Isaiah 44:2) a symbolical name for Israel in ( 32:15; 33:5,26; Isaiah 44:2) It is most probably derived from a root signifying "to be blessed." With the intensive termination Jeshurun would then denote Israel as supremely happy or prosperous, and to this signification the context in ( 32:15) points.
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Smith, William, Dr. "Entry for 'Jesh’urun'". "Smith's Bible Dictionary".