Concluded it's to do with (4)
I believe the answer is:
over
I believe this clue is a double definition.
'concluded' is the first definition.
(synonyms)
'to do with' is the second definition.
(both can mean relating to or as a result of)
'it's' is the link.
(Other definitions for over that I've seen before include "In the sky?" , "Unit of test" , "Action far more drastic than necessary" , "Completely ended" , "Finished, concluded" .)