Cliff is the opposite of Plain. Plain is related to Regular. Regular is a type of Patron. 
Curve is a different concept from Square. Square is related to Lift. Lift is related to Weight. Weight is a type of Importance. 
Cliff <--Antonym--> Plain <--RelatedTo--> Regular --IsA--> Patron 
Curve <--DistinctFrom--> Square <--RelatedTo--> Lift <--RelatedTo--> Weight --IsA--> Importance 