Relating to kidneys (5)
I believe the answer is:
renal
'relating to kidneys' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for renal that I've seen before include "associated with organ" , "Pertaining to the kidney" , "Vital organ's" , "Learn (anag) - of organs of the body" , "connected with organ" .)