Dirt is a synonym of Soil. 
Certain is the opposite of Impossible. Impossible is a different concept from Able. Able is related to Possible. Possible is a synonym of Option. 
Dirt <--Synonym--> Soil 
Certain <--Antonym--> Impossible <--DistinctFrom--> Able <--RelatedTo--> Possible <--Synonym--> Option 