Purchase is a synonym of Buy. Buy is related to Transaction. Transaction is related to Trade. Import is a type of Trade. 
Secret is related to Desire. Desire is related to Regret. 
Purchase <--Synonym--> Buy <--RelatedTo--> Transaction <--RelatedTo--> Trade <--IsA-- Import 
Secret <--RelatedTo--> Desire <--RelatedTo--> Regret 