The Collaborative International Dictionary of English v.0.48:

Polysilicic \Pol`y*si*lic"ic\, a. [Poly- + silicic.] (Chem.)
   Of or pertaining to compounds formed by the condensation of
   two or more molecules of silicic acid.
   [1913 Webster]

   Polysilicic acid (Chem.), any one of a series of acids
      formed by the condensation of two or more molecules of
      silicic acid, with elimination of water.
      [1913 Webster]