fluosilicic : Idioms & Phrases

• noun an unstable poisonous corrosive acid known primarily in the form of its salts
  hydrofluosilicic acid.
  

WordNet

• 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.

Webster 1913