An Etymological Dictionary of the German Language/Harn
Harn, m., ‘urine,’ earlier dial. variant Harm (Luther), from MidHG. harn (Bav. and East Rhen.), harm, m. and n., OHG. haran, m., ‘urine’ (respecting the variant with m see Farn); a specifically UpG. word, probably identical orig. with AS. scearn, OIc. skarn, n., ‘mud’; sk and h (the latter for k without s) would have interchanged in OTeut. Allied to Gr. σκώρ; comp. hocken, drosseln, links, Stier. The derivation of Harn from a root har, ‘to pour out,’ remains dubious.