A leading light naturally (5,4)
I believe the answer is:
north star
'a leading' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'light naturally' is the wordplay.
I cannot really understand how this works, but
'light' could be 'star' (I have seen 'Heavenly light ' mean 'star' so perhaps 'light' could also mean 'star') and 'star' is found in the answer.
The remaining letters 'north' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for north star that I've seen before include "nickname of US State" , "guiding light" , "navigational guide" , "Polaris" , "Navigational aid" .)