The Collaborative International Dictionary of English v.0.48:

Prussian \Prus"sian\, a. [From Prussia, the country: cf. F.
   prussien.]
   Of or pertaining to Prussia. -- n. A native or inhabitant of
   Prussia.
   [1913 Webster]

   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 (Zool.) See Gibel.

   Prussian green. (Chem.) Same as Berlin green, under
      Berlin.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Blue \Blue\ (bl[=u]), n.
   1. One of the seven colors into which the rays of light
      divide themselves, when refracted through a glass prism;
      the color of the clear sky, or a color resembling that,
      whether lighter or darker; a pigment having such color.
      Sometimes, poetically, the sky; as, to fly off into the
      blue.
      [1913 Webster]

   2. A pedantic woman; a bluestocking. [Colloq.]
      [1913 Webster]

   3. pl. [Short for blue devils.] Low spirits; a fit of
      despondency; melancholy. [Colloq.]
      [1913 Webster]

   Berlin blue, Prussian blue.

   Mineral blue. See under Mineral.

   Prussian blue. See under Prussian.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Prussian blue
    n 1: any of various blue pigments [syn: iron blue, Prussian
         blue]
    2: a dark greenish-blue color