碱（jiǎn）是一种化学物质，具有碱性的性质。它通常指的是氢氧化物或碳酸盐等化合物，在水溶液中能够产生氢离子的化合物。

How to pronounce: jiǎn [dʒiɛn]

Usage:

1. In chemistry, bases are substances that can neutralize acids and have a pH greater than 7.

2. In everyday language, bases are often referred to as alkaline substances.

Example sentences:

1. The cleaning product contains a high concentration of alkali, which helps to remove stubborn stains.

这种清洁产品含有高浓度的碱，可以帮助去除顽固污渍。

2. The soil in this area is alkaline, making it suitable for growing certain types of plants.

这个地区的土壤是碱性的，适合种植某些类型的植物。

Synonyms and usage:

1. Alkali: another term for base, used more commonly in chemistry.

2. Lye: a strong alkali used in soap-making and other industrial processes.

3. Caustic: a strong chemical base that can cause burns or corrosion.

4. Basic: having a pH greater than 7; can also refer to something simple or fundamental.

5. Alkaline: having a pH greater than 7; often used to describe substances or environments.

Editor's summary:

In summary, the term "base" refers to a chemical substance with alkaline properties that can neutralize acids and has a pH greater than 7. It is commonly used in chemistry and everyday language to describe substances with these characteristics. Synonyms for base include alkali, lye, caustic, basic, and alkaline. It is important to note that bases can be dangerous and should be handled with caution.