Deich.

From Middle Low German dīk, from Old Saxon dīk, from Proto-West Germanic *dīk, from Proto-Germanic *dīkaz. Originally the same word as Teich (“pond”). The sense “dike” spread via Low German, for which reason the form Deich is most often regarded as an artificial adaptation of Middle Low German dīk (“dike”) to the phonetic system of standard German. However, Deich is also the form natively developed in West Central German and it does mean “dike, dam, weir system” in most dialects of the Rhineland, particularly along the Lower Rhine. The supposition of an artificial adaptation is therefore possible but not inevitable. Cognate to Dutch dijk, to West Frisian dyk, to English dyke, dike and to Saterland Frisian Diek.