Alkalify is a verb meaning to make something more alkaline or basic. The opposite or antonym of alkalify would be to acidify, which means to increase the acidity or lower the pH of a substance. Acidify can also mean to add acid to a substance. Other antonyms of alkalify include neutralize, which means to bring something to a neutral state; deacidify, which means to make something less acidic; and sour, which means to make something acidic or sour-tasting. These antonyms are used in various contexts, such as in chemistry, cooking, and agriculture, where the pH level of a substance is important.