- a very hard almost colourless crystalline metalloid element that in impure form exists as a brown amorphous powder. It occurs principally in borax and is used in hardening steel. The naturally occurring isotope boron-10 is used in nuclear control rods and neutron detection instruments. Symbol: B; atomic no: 5; atomic wt: 10.81; valency: 3; relative density: 2.34 (crystalline), 2.37 (amorphous); melting pt: 2092°C; boiling pt: 4002°C
WordReference Random House Learner's Dictionary of American English © 2017
- Chemistrya nonmetallic element occurring in nature only in combination, as in borax or boric acid, and used in alloys and nuclear reactors.
- Chemistrya nonmetallic element occurring naturally only in combination, as in borax or boric acid, and obtained in either an amorphous or a crystalline form when reduced from its compounds. Symbol: B; at. wt.: 10.811;
at. no.: 5.
- bor(ax1) + (carb)on 1805–15