An Etymological Dictionary of the German Language/Annotated/osten

osten, adverb, from Middle High German ôsten, ôstene, ‘in, to, or from the east,’ Old High German ôstana, ‘from the east,’ so too Anglo-Saxon eástene, ‘in the east,’ eástan, ‘from the east,’ Old Saxon ôstan, ôstana, ‘from the east’; Old High German and Old Saxon ôstar, ‘to the east.’ The stem austa- (in Old Icelandic austr, genitive austrs, masculine), on which these words are based, is undoubtedly connected with the Old Aryan term for ‘dawn’; primitively Aryan *ausôs, Sanscrit ušâs, Latin aurôra (for *ausôs-a), Greek ἠώς, Lithuanian auszrà, ‘dawn.’ Since, in other instances, the names for the periods of the day have been applied to the cardinal points, e.g., Mittag, Morgen, &c., the dawn might be used for the east, especially as Morgen in Upper German signifies ‘east’ (in Upper German the old terms for the cardinal points are almost obsolete). Compare also Ostern.