Source : Webster's Revised Unabridged Dictionary (1913)

Prussian \Prus"sian\, a. [From Prussia, the country: cf. F.
   prussien.]
   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} (Zo["o]l.) See {Gibel}.

   {Prussian green}. (Chem.) Same as {Berlin green}, under
      {Berlin}.

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.

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

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

   {Berlin blue}, Prussian blue.

   {Mineral blue}. See under {Mineral}.

   {Prussian blue}. See under {Prussian}.

Source : WordNet®

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