In the long run it yields oneness (5)
I believe the answer is:
unity
'oneness' is the definition.
(I know that oneness can be written as unity)
'in the long run it yields' is the wordplay.
'in' says the answer is hidden in the clue.
'UNITY' can be found hidden inside 'long run it yields'.
(Other definitions for unity that I've seen before include "One of the Mitfords" , "State of being joined as a whole" , "Number one" , "State of togetherness" , "Oneness, harmony" .)