An Etymological Dictionary of the German Language/Annotated/Osten
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Osten, masculine, from the equivalent Middle High German ôsten, masculine and neuter, Old High German ôstan, masculine and neuter, ‘east’; the form Ost is wanting in Middle High German and Old High German; it has probably been recently coined; compare Nord and Norden, Süd and Suden, West and Westen. Yet even in Anglo-Saxon eást, English east, occurs, whence French est. —