acidity has 3 distinct synonyms spread across 2 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is alkalinity.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the property of being acidic
the taste experience when something acidic is taken into the mouth
pH values below 7
Synonyms, antonyms and the broader and narrower relations for acidity come from Princeton University’s WordNet. Full sources and licences.