Buy is related to Obtain. Derive is a type of Obtain. Derive is a type of Make. Prepare is a type of Make. 
Weird is related to Odd. Odd is the opposite of Normal. Normal is related to Regular. Regular is a type of Soldier. 
Buy <--RelatedTo--> Obtain <--IsA-- Derive --IsA--> Make <--IsA-- Prepare 
Weird <--RelatedTo--> Odd <--Antonym--> Normal <--RelatedTo--> Regular --IsA--> Soldier 