Casual is the opposite of Necessary. Necessary is related to Permit. Permit is related to License. License is a type of Permission. 
Repeat is a synonym of Reinforce. Reinforce is a synonym of Instruct. 
Casual <--Antonym--> Necessary <--RelatedTo--> Permit <--RelatedTo--> License --IsA--> Permission 
Repeat <--Synonym--> Reinforce <--Synonym--> Instruct 