The Collaborative International Dictionary of English v.0.48:

Prussiate \Prus"si*ate\, n. [Cf. F. prussiate.] (Chem.)
   A salt of prussic acid; a cyanide.
   [1913 Webster]

   Red prussiate of potash. See Potassium ferricyanide,
      under Ferricyanide.

   Yellow prussiate of potash. See Potassium ferrocyanide,
      under Ferrocyanide.
      [1913 Webster]

WordNet (r) 3.0 (2006):

yellow prussiate of potash
    n 1: a cyanide compound that is prepared by the reaction of
         potassium cyanide with ferrous salts; commonly used by
         gardeners [syn: potassium ferrocyanide, yellow prussiate
         of potash]