ren
n. countable C2 Proficiency US //ˈɹɛn// ren
n. a person's kidney. This is a very old or technical word that you will mostly see in medical terms or old books.
n. the kidney, or a part of the body relating to the kidney. Primarily used in anatomical contexts or as a root in medical terminology; archaic in general prose.
The doctor checked the health of the patient's ren.
In older medical texts, the term ren was frequently used before 'kidney' became the standard English word.
While modern practitioners refer to the kidney, the Latin root survives in the adjective 'renal', which describes anything pertaining to the function or pathology of the ren.
Usage
Rarely used as a standalone noun in modern English; typically appears as a root in medical adjectives like 'renal'.