Source : Webster's Revised Unabridged Dictionary (1913)

Borosilicate \Bo"ro*sil"i*cate\, n. [Boron + silicate.] (Chem.)
   A double salt of boric and silicic acids, as in the natural
   minerals tourmaline, datolite, etc.

Source : WordNet®

borosilicate
     n : a salt of boric and silicic acids