Central is related to Main. Main is related to Floor. Floor is a synonym of Story. Story is related to Plot. 
Hospital is related to Emergency. Emergency is a synonym of Casualty. Casual is derived from Casualty. 
Central <--RelatedTo--> Main <--RelatedTo--> Floor <--Synonym--> Story <--RelatedTo--> Plot 
Hospital <--RelatedTo--> Emergency <--Synonym--> Casualty <--DerivedFrom-- Casual 