Run for so long (3)
I believe the answer is:
bye
This clue is a double definition.
'run' is the first definition.
(type of cricket run)
'for so long' is the second definition.
(synonyms)
(Other definitions for bye that I've seen before include "Stay out of round" , "Law of the local authority" , "Run scored in cricket from unhit ball" , "I'm off" , "Farewell! (informal)" .)