Rack is etymologically related to Rock. Rack is a type of Fly. 
Role is related to Character. Character is related to True. True is similar to Sure. Sure is a synonym of Reliable. 
Rock <--EtymologicallyRelatedTo-- Rack --IsA--> Fly 
Role <--RelatedTo--> Character <--RelatedTo--> True <--SimilarTo--> Sure <--Synonym--> Reliable 