- 1a substance with particular chemical properties including turning litmus red, neutralizing alkalis, and dissolving some metals; typically, a corrosive or sour-tasting liquid of this kind: trees were exposed to mixtures of heavy metals, acids, and overdoses of nutrients [mass noun]:traces of acidOften contrasted with alkali and base1.
Acids are compounds which release hydrogen ions (H+) when dissolved in water. Any solution with a pH of less than 7 is acidic, strong acids such as sulphuric or hydrochloric acid having a pH as low as 1 or 2
- Australian/NZ informal seek to extract a loan or favour from (someone).[acid from acid test, referring to possible resistance (because gold resists nitric acid)]
early 17th century (in the sense 'sour-tasting'): from Latin acidus, from acere 'be sour'