Bag is related to Stuff. Stuff is related to Matter. Matter is a synonym of Substance. Medium is a type of Substance. 
Smile is related to Subtle. Subtle is the opposite of Simple. Simple is the opposite of Compound. 
Bag <--RelatedTo--> Stuff <--RelatedTo--> Matter <--Synonym--> Substance <--IsA-- Medium 
Smile <--RelatedTo--> Subtle <--Antonym--> Simple <--Antonym--> Compound 