corundum

詳細解釋：

co.run.dum

n.（名詞）
An extremely hard mineral, aluminum oxide, Al2O 3, sometimes containing iron, magnesia, or silica, that occurs in gem varieties such as ruby and sapphire and in a common black, brown, or blue form used chiefly in abrasives.
剛玉：一種極為堅硬的礦物，氧化鋁，Al2O 3，有時含鐵、氧化鎂或矽土，存在於各種寶石中，如紅寶石、藍寶石，並且在磨蝕劑中以普通的黑色、棕色或藍色形式出現

來源：
Tamil kuruntam
泰米爾語 kuruntam