Kind of system operating in body, giving directions on timeless principle (9)
I believe the answer is:
endocrine
'kind of system operating in body' is the definition.
(as in the body's endocrine system)
'directions on timeless principle' is the wordplay.
I cannot quite see how this works, but
'directions' could be 'ne' (I've seen this in other clues) and 'ne' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'giving' acts as a link.
Can you help me to learn more?
(Another definition for endocrine that I've seen is " Of gland, secreting straight into blood and not through duct".)