Meaning

noun either of two bean-shaped excretory organs that filter wastes (especially urea) from the blood and excrete them and water in urine

originFrom Middle English kideney, kydeney, alteration of earlier kidenere (“kidney”) after ey (“egg”), of obscure origin and formation. Probably a compound consisting of Middle English *kidde (“sack”) + Middle English nere (“kidney”). The first element would be from Old English *cydde (“sack, scrotum”), from Proto-Germanic *kuddijā (“sack”), as the terms for testicle and kidney were often…

Etymology from Wiktionary, CC BY-SA 3.0