Promise is etymologically related to Permit. Permit is a synonym of Prohibit. Prohibit is a synonym of Forbid. 
Helpful is related to Cooperative. Cooperative is a type of Association. League is a type of Association. 
Promise --EtymologicallyRelatedTo--> Permit <--Synonym--> Prohibit <--Synonym--> Forbid 
Helpful <--RelatedTo--> Cooperative --IsA--> Association <--IsA-- League 