Accident is a synonym of Casualty. Casualty is a type of Decrease. Decrease is the opposite of Soar. Soar is a type of Rise. 
Hill is related to Landmark. Landmark can be used for Learn. 
Accident <--Synonym--> Casualty --IsA--> Decrease <--Antonym--> Soar --IsA--> Rise 
Hill <--RelatedTo--> Landmark --UsedFor--> Learn 