Plattdeutsch
noun
Platt·deutsch ˈplat-ˌdȯich 
ˈplät-
ˈplät- : the Low German speech of northern Germany comprising several dialects
Word History
Etymology
German, from Dutch Platduitsch, literally, Low German, from plat flat, low + duitsch German
First Known Use
1677, in the meaning defined above