Early 19th century. From German Platt Low German, also used of other regional varieties of German in general sense ‘dialect’, probably partly from an extended sense of platt flat, low, and partly shortened from Plattdeutsch.
Definition of Platt in US English:
Platt
nounplat
Plattdeutsch.
Origin
Early 19th century. From German Platt Low German, also used of other regional varieties of German in general sense ‘dialect’, probably partly from an extended sense of platt flat, low, and partly shortened from Plattdeutsch.