An Etymological Dictionary of the German Language/Annotated/fließen
fließen, verb, ‘to flow, stream,’ from the equivalent Middle High German vlieȥen, Old High German flioȥȥan, strong verb; corresponds to Old Saxon fliotan, Dutch vlieten, Anglo-Saxon fleótan, English to fleet, Old Icelandic fljóta, Gothic *fliutan, ‘to flow.’ The Teutonic root fliut, flut, from pre-Teutonic pleud-plud, corresponds to Lettic pludêt, ‘to float,’ plûdi, inundation,’ Lithuanian plústi, ‘to take to swimming,’ plûdìs, ‘floating wood.’ Several Teutonic terms for ‘ships’ point to the latter sense, which, of course, is earlier than the Modern High German ‘flowing,’ though in Old High German Middle High German and Modern High German, fließen signifies ‘to be driven by flowing water, to swim.’ See Floß, Flotte (Flut, Gothic flôdus, is not a cognate). Instead of the root plud, other Aryan languages have an allied shorter root plu; compare Greek πλέω, ‘to navigate, swim,’ Sanscrit plu, pru, ‘to swim,’ Latin pluere, ‘to rain’ (fließen in a restricted sense).