PlattdeutschyoudaoicibaDictYouDict[Plattdeutsch 词源字典]
"Low German dialect of northern Germany," 1814, from German, from Dutch platduits, literally "flat (or low) German," from plat "flat, plain, clear" + duits "German" (see Dutch). In contrast to the speech of the upland parts of Germany.[Plattdeutsch etymology, Plattdeutsch origin, 英语词源]