Moon is related to Full. Full is the opposite of Partial. 
Butt is a synonym of Target. Target is similar to Source. Source is related to River. River is related to Mouth. 
Moon <--RelatedTo--> Full <--Antonym--> Partial 
Butt <--Synonym--> Target <--SimilarTo--> Source <--RelatedTo--> River <--RelatedTo--> Mouth 