An Etymological Dictionary of the German Language/Annotated/ein
ein, numeral, from the equivalent Middle High German and Old High German ein, ‘one,’ also the indefinite article even in Old High German and Middle High German; compare Old Saxon én, Dutch een, Anglo-Saxon ân (English one, as a numeral a, an, as indefinite article), Old Icelandic einn, Gothic ains. The numeral common to Teutonic for ‘one,’ originally ainos, which is primitively cognate with Latin ûnus (compare commûnis and gemein, ‘common’), and also with Old Irish óen, Old Slovenian inŭ, Lithuanian vënas, Prussian ains, ‘one.’ From this old numeral, which strangely enough is unknown to East Aryan (in which the cognate terms Sanscrit êka, Zend aéva, ‘one,’ occur), Greek (dialectic) has preserved οἰνός, ‘one,’ and οἴνη, ‘the one on dice, ace.’ See Eiland, Einöde. —