Unit is related to Memory. Memory is related to Picture. Picture is similar to Image. 
Usual is a synonym of Common. Common is the opposite of Royal. Royal is related to Elegant. 
Unit <--RelatedTo--> Memory <--RelatedTo--> Picture <--SimilarTo--> Image 
Usual <--Synonym--> Common <--Antonym--> Royal <--RelatedTo--> Elegant 