Learn arrangement of the kidneys (5)
I believe the answer is:
Here is my best explanation:
'of the kidneys' is the definition.
(I've seen this before)
'learn arrangement' is the subsidiary indication.
'arrangement' indicates an anagram.
'learn' is an anagram of 'renal'.
(Other definitions for renal that I've seen before include "associated with organ", "Organ's", "Learn (anag) - of organs of the body", "relating to the kidneys", "Concerned with organ", "Of the kidneys", "Referring to organ", "Pertaining to the kidneys", "Vital organ's" and "using the reins".)