The Collaborative International Dictionary of English v.0.48:

Fluosilicic \Flu`o*si*lic"ic\, a. [Fluo- + silicic: cf. F.
   fluosilicique.] (Chem.)
   Composed of, or derived from, silicon and fluorine.
   [1913 Webster]

   Fluosilicic acid, a double fluoride of hydrogen and
      silicon, H2F6Si, obtained in solution in water as a sour
      fuming liquid, and regarded as the type of the
      fluosilicates; -- called also silicofluoric acid, and
      hydrofluosilicic acid.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fluosilicic acid
    n 1: an unstable poisonous corrosive acid known primarily in the
         form of its salts [syn: fluosilicic acid,
         hydrofluosilicic acid]