Steam is the opposite of Ice. Ice is related to Frozen. Frozen is a synonym of Fixed. Fixed is the opposite of Mobile. 
Unusual is similar to Unique. Unique is related to Continent. 
Steam <--Antonym--> Ice <--RelatedTo--> Frozen <--Synonym--> Fixed <--Antonym--> Mobile 
Unusual <--SimilarTo--> Unique <--RelatedTo--> Continent 