<p><strong>Noun</strong></p><ul><li>The natural or synthetic oxide of aluminum, Al₂O₃, occurring in nature in a pure crystal form as corundum.</li><li>A crystalline solid, aluminum potassium sulfate, K₂SO₄·Al₂(SO₄)₃·24H₂O, used in medicine as an astringent and styptic, in dyeing and tanning, and in many technical processes.</li><li>One of a class of double sulfates analogous to aluminum potassium sulfate, as aluminum ammonium sulfate, having the general formula R₂SO₄·X₂(SO₄)₃·24H₂O, where R is a univalent alkali metal or ammonium, and X one of a number of trivalent metals.</li></ul>