Native alumina or aluminium sesquioxide, Al2O3; corundum; esp., the blue transparent variety of corundum, highly prized as a gem.
- A clear hard variety of corundum used as a gemstone that is usually blue but may be any color except red.
- A corundum gem.
- The blue color of a gem sapphire.
- Made of or resembling a gem sapphire.
- Having the color of a blue sapphire.