What does "prussian" mean?

Prussian: Of or pertaining to Prussia. -- n. A native or inhabitant of Prussia. Prussian blue (Chem.), any one of several complex double cyanides of ferrous and ferric iron; specifically, a dark blue amorphous substance having a coppery luster, obtained by adding a solution of potassium ferrocyanide (yellow prussiate of potash) to a ferric salt. It is used in dyeing, in ink, etc. Called also Williamson's blue, insoluble Prussian blue, Berlin blue, etc. -- Prussian carp (Zoöl.) See Gibel. -- Prussian green. (Chem.) Same as Berlin green, under Berlin.