An Etymological Dictionary of the German Language/Annotated/sich

by Friedrich Kluge

sich, pronoun, ‘himself, herself,’ &c., from the equivalent Middle High German sich, accusative and dative, Old High German sih, accusative; corresponding to the equivalent Old Low German and Gothic sik, accusative. Compare Latin se, Greek ἐ, Old Slovenian sę, accusative, ‘himself,’ &c. (sebě, dative, like Latin sibi); Sanscrit sva, ‘own,’ Latin suus, Greek ἑός, ὅς. Hence even in Aryan there existed a reflex. pronoun sve-, se-. Further details belong to grammar.