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 "Explanation; logic", "issue", "Ability to think rationally", "Think in a logical way", "Cause or motive", "Cause, justification", "Logic and rationality", "An explanation", "Power of thought" and "Reach logical conclusions".)