"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 (High German).
platitude
Platonic
Platonism
Platonist
platoon
Plattdeutsch
platter
platypus
plaudit
plausibility
plausible