Warn is a type of Advise. Advise is a synonym of Counsel. Counsel is a synonym of Tip. Tip is a synonym of Upset. 
Nightmare is a synonym of Horror. Horror is related to Genre. Genre is a synonym of Class. 
Warn --IsA--> Advise <--Synonym--> Counsel <--Synonym--> Tip <--Synonym--> Upset 
Nightmare <--Synonym--> Horror <--RelatedTo--> Genre <--Synonym--> Class 