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.

• A white or gray/grey crystalline salt, with a slight alkaline taste, used as a flux, in soldering metals, making enamels, fixing colors/colours on porcelain, and as a soap.