Ban is a synonym of Prohibit. Prohibit is the opposite of Let. Let is related to Admit. Admit is the opposite of Denial. 
Ash is a type of Change. Convert is a type of Change. 
Ban <--Synonym--> Prohibit <--Antonym--> Let <--RelatedTo--> Admit <--Antonym--> Denial 
Ash --IsA--> Change <--IsA-- Convert 