The words small, white, and kidney may seem difficult to find antonyms for, but with a little creativity, there are several options. To start, the opposite of small could be large or big. In contrast, the opposite of white might be black, dark, or colorful. Lastly, the word kidney could be paired with antonyms such as heart or lungs, as they are all organs. Putting it all together, some possible antonyms for small white kidney could be: large colorful heart, big dark lungs, or any combination of opposites that may suit the context.