1. A compound yielding a hydrogen ion in a polar solvent (e.g., in water); acids form salts by replacing all or part of the ionizable hydrogen with an electropositive element or radical.

2. In popular language, any chemical compound that has a sour taste (given by the hydrogen ion).

3. Sour; sharp to the taste.

4. Relating to acid; giving an acid reaction. For individual acids, see specific names.


[L. acidus, sour]

bile acids

Brønsted acid

conjugate acid

dibasic acid

inorganic acid

Lewis acid

monobasic acid

organic acid

polybasic acid

ruberythric acid

wax acid