The quality or state of being acid, in taste or in chemical properties (or both); sourness, sharpness to the taste. Also: the degree to which a substance, medium, etc., is acid (acid adj. 2a), esp. (Chemistry) as measured by hydrogen-ion concentration or pH. Also: an instance of acid properties, an acid substance. Cf. acid adj. 1a, 2a.——牛津当代大辞典

a chemical substance that has a pH of less than 7. Strong acids can burn holes in material or damage your skin.——朗文当代大辞典

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