Clean is the opposite of Mark. Stake is a type of Mark. Stake is related to Killing. 
Grass is related to Seed. Seed is related to Bay. Bay is related to Front. 
Clean <--Antonym--> Mark <--IsA-- Stake <--RelatedTo--> Killing 
Grass <--RelatedTo--> Seed <--RelatedTo--> Bay <--RelatedTo--> Front 