Unusual is similar to Extraordinary. Extraordinary is the opposite of Common. 
Free is related to Open. Open is a synonym of Capable. Capable is derived from Ability. Sensitivity is a type of Ability. 
Unusual <--SimilarTo--> Extraordinary <--Antonym--> Common 
Free <--RelatedTo--> Open <--Synonym--> Capable --DerivedFrom--> Ability <--IsA-- Sensitivity 