Dictionary
co•run•dum
Pronunciation: (ku-run'dum), [key]—
n.
a common mineral, aluminum oxide, Al
2O
3, notable for its hardness: transparent varieties, as sapphire and ruby, are used as gems, other varieties as abrasives: often made synthetically.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.