The Collaborative International Dictionary of English v.0.48:

Borax \Bo"rax\, n. [OE. boras, fr. F. borax, earlier spelt
   borras; cf. LL. borax, Sp. borraj; all fr. Ar. b?rag, fr.
   Pers. b?rah.]
   A white or gray crystalline salt, with a slight alkaline
   taste, used as a flux, in soldering metals, making enamels,
   fixing colors on porcelain, and as a soap. It occurs native
   in certain mineral springs, and is made from the boric acid
   of hot springs in Tuscany. It was originally obtained from a
   lake in Thibet, and was sent to Europe under the name of
   tincal. Borax is a pyroborate or tetraborate of sodium,
   Na2B4O7.10H2O.
   [1913 Webster]

   Borax bead. (Chem.) See Bead, n., 3.
      [1913 Webster]

WordNet (r) 3.0 (2006):

borax
    n 1: an ore of boron consisting of hydrated sodium borate; used
         as a flux or cleansing agent