1. a soluble salt or mixture of salts found in some soils and capable of neutralizing acids; a substance that turns litmus paper blue
Usage: chemistry; commonly used in scientific and industrial contexts
2. any of various soluble mineral salts, especially sodium carbonate or potassium carbonate, obtained from wood ash or natural deposits
Usage: historical; industrial

Examples

• The soil in that region contains too much alkali for most crops to grow well.
• Alkali reacts with acid to form water and a salt.
• The chemist added alkali to the solution to raise its pH.
• Historically, alkali was extracted from wood ash and used in soap making.
• An alkali turns red litmus paper blue, which is a key test in chemistry class.
• The desert lake's water is rich in alkali minerals.
• Baking soda is a mild alkali commonly used in cooking and cleaning.