Agreed it's over (4)
I believe the answer is:
done
I believe this is a double definition.
'agreed' is the first definition.
(I've seen this before)
'over' is the second definition.
(both can mean finished)
'it's' is the link.
(Other definitions for done that I've seen before include "(Of food) well cooked" , "See 23" , "This settled" , "Artist's workroom" , "Robbed" .)