Sum is a synonym of Union. Union is a synonym of Join. Join is the opposite of Split. 
Operating is related to Window. Window is a type of Panel. Panel is related to Council. Council is related to Board. 
Sum <--Synonym--> Union <--Synonym--> Join <--Antonym--> Split 
Operating <--RelatedTo--> Window --IsA--> Panel <--RelatedTo--> Council <--RelatedTo--> Board 