Moving so near ground (6)
I believe the answer is:
Here is my best explanation:
'ground' is the definition.
('reason' can be a synonym of 'ground')
'moving so near' is the subsidiary indication.
'moving' indicates anagramming the letters.
'sonear' is an anagram of 'reason'.
(Other definitions for reason that I've seen before include "Mental power to justify an act", "Ability to think rationally", "Sanity and logic", "Sense", "Justification or motive", "Cause; mind's power", "Motive or right thinking", "Rational motive", "Think logically" and "Purpose".)