An Etymological Dictionary of the German Language/Annotated/Arsch
Arsch, masculine, ‘arse, fundament,’ according to the analogous cases cited under birschen, from an older Ars, Middle High German and Old High German ars, masculine, ‘arse.’ It corresponds to the equivalent Middle Low German ars, ers, Dutch aars, naars (with prefixed n), Anglo-Saxon ears, English arse, Old Icelandic ars (and rass, compare argr and ragr, see arg), masculine, ‘arse.’ Teutonic arsa-z, masculine, from órso-s, is rightly held to be primitively allied to Greek δῥῥος (ρρ for rs), ‘coccyx, rump’; akin to Old Irish err, feminine, ‘tail, end, point’?. Compare the remark under Arm.