An organ in the body that filters the blood, producing urine.
This organ (of an animal) cooked as food.
(figuratively, dated) Constitution, temperament, nature, type, character, disposition. (usually used of people)
30th June, 1788, Robert Burns, letter to Mr Robert Ainslie
Your poets, spendthrifts, and other fools of that kidney, pretend, forsooth, to crack their jokes on prudence.