One near it may show lethargy (7)
I believe the answer is:
inertia
'lethargy' is the definition.
(both can mean a lack of movement)
'one near it may show' is the wordplay.
'one' becomes 'i' (Roman numeral).
'may show' indicates anagramming the letters.
'near'+'it'='nearit'
'nearit' anagrammed gives 'nertia'.
'i'+'nertia'='INERTIA'
(Other definitions for inertia that I've seen before include "Tendency not to act" , "Sluggishness - sloth" , "Sort of reel" , "showing reluctance to move" , "A disposition to remain inactive" .)