Serious is a synonym of Grave. Grave is related to Dead. Dead is related to Stick. Stick is related to Ball. 
Equality is the opposite of Difference. Difference is related to Miss. Miss is related to Fail. 
Serious <--Synonym--> Grave <--RelatedTo--> Dead <--RelatedTo--> Stick <--RelatedTo--> Ball 
Equality <--Antonym--> Difference <--RelatedTo--> Miss <--RelatedTo--> Fail 