Definition of "ren"

Having treated laſt of the expulſion of the inteſtinal fæces, we come next to conſider thoſe organs, which ſeparate and throw off another principal excrementitious matter, to wit, urine. The firſt of which is the renes or kidneys.

1759, Malcolm Flemyng, “Lecture XIX. On the kidneys and urinary bladder. Gravel; calculus.”, in An Introduction to Physiology, Being a Courſe of Lectures Upon the moſt important Parts of the Animal Œconomy: […], London: J. Nourse, page 259

We find, however, that the detrita, consisting principally of effete hydrogen and carbon, brought into the circulation by the absorbents, are constantly making their escape from the system by way of the renes, skin, and lungs, in the forms of water, and carbonic-acid.

1810, William Tully, “On Aliment”, in Proceedings of the Presidents and Fellows of the Connecticut Medical Society, published 1884, page 326

It would probably have been considered an important omission if I had not mentioned Water as a substance excreted freely by the renes or kidneys.

1858, William Tully, Materia Medica; Or, Pharmacology and Therapeutics, page 1195

Renal. Belonging to the ren or kidney.

1893, Henry Power, Leonard William Sedgwick, The New Sydenham Society's Lexicon of Medicine and the Allied Sciences

For the Ren did not belong to the man, but came out of the Celestial Waters to enter an infant in the hour of his birth and might not stir again until it was time to go back.

1983, Norman Mailer, Ancient Evenings