Acidness is a term that refers to the quality of being sour or acidic. Its antonym, therefore, would be something that is the opposite of sour, meaning it has a more palatable and pleasant taste. The word "alkalinity" is a suitable antonym for acidness, as it describes the quality of being alkaline or basic. Other antonyms for acidness might include words such as sweetness, mildness, or blandness, all of which describe qualities that are the opposite of sourness. While the term acidness is typically used to describe the taste of food or drink, its antonyms may also be used in other contexts to describe things like personality traits or emotions.