Toll is etymologically related to Tale. Toll is a synonym of Duty. Duty is related to Must. Must is related to Important. 
Unit is etymologically related to Unity. Unit is related to Single. Hurricane is a type of Single. Hurricane is related to Rain. 
Tale <--EtymologicallyRelatedTo-- Toll <--Synonym--> Duty <--RelatedTo--> Must <--RelatedTo--> Important 
Unity <--EtymologicallyRelatedTo-- Unit <--RelatedTo--> Single <--IsA-- Hurricane <--RelatedTo--> Rain 