An Etymological Dictionary of the German Language/waschen
waschen, vb., ‘to wash,’ from the equiv. MidHG. waschen (węschen), OHG. wascan, str. vb.; comp. Du. wasschen, AS. wasčan, E. to wash, OIc. vaska (Goth. *waskan), ‘to wash.’ The sk of the old forms was orig. only a part of the present stem, but was afterwards joined to the base; it may have been preceded by a dental. Teut. *watska- probably based on the Teut. nominal stem wat, ‘water’ (see Wasser); comp. OIr. usce, ‘water’ Ir. faiscim, W. gwasgu, ‘I press,’ may, however, with equal reason, be connected with waschen.