An Etymological Dictionary of the German Language/sinken
sinken, vb., ‘to sink, fall, abate,’ from the equiv. MidHG. sinken, OHG. sinchan; a common Teut. str. vb. (for its causative see senken). Comp. Goth. sigqan, OIc. sokkra, AS. sincan, E. to sink, Du. zinken, OSax. sincan. The a-root senq, contained in these words, seems to have originated in an i-root sī̆q, which appears in the parallel form sī̆hw in ModHG. seihen, as well as OHG. sîgan, MidHG. sîgen, ‘to drip.’ The pre-Teut. root sig, siq appears in OSlov. sĭcati, ‘to make water,’ sĭčĭ}, ‘urine,’ as well as in Sans. sic, ‘to wet, pour out,’ whose pres. appears in a nasalised form ModHG. seihen is based upon Teut. saik, pre-Teut. síg.