An Etymological Dictionary of the German Language/du
Appearance
du, 2nd pers. pron., ‘thou’; from MidHG. and OHG. du, and the collateral MidHG. and OHG. dû; comp. AS. þû, E. thou; Lat. tu, Gr. τύ, σύ, and Sans. tvam, are prim. cognates. The details respecting the Aryan pronom. stem belong to grammar.