The Collaborative International Dictionary of English v.0.48:

Silundum \Si*lun"dum\, n. [Trade name]
   A form of silicon carbide, produced in the electric furnace,
   possessing great hardness, and high electrical resistance,
   and not subject to oxidation below 2880[deg] F., or 1600[deg]
   C.
   [Webster 1913 Suppl.]