Towel is a type of Wipe. Wipe is related to Wash. Wash is the opposite of Dirty. Dirty is related to Waste. 
Necessary is a synonym of Fatal. 
Towel --IsA--> Wipe <--RelatedTo--> Wash <--Antonym--> Dirty <--RelatedTo--> Waste 
Necessary <--Synonym--> Fatal 