Custom is a synonym of Tax. Tax is related to Transaction. Transaction is related to Call. 
Flavor is related to Cake. Cake is related to Receive. Receive is related to Exchange. Exchange is a type of Conversation. 
Custom <--Synonym--> Tax <--RelatedTo--> Transaction <--RelatedTo--> Call 
Flavor <--RelatedTo--> Cake <--RelatedTo--> Receive <--RelatedTo--> Exchange --IsA--> Conversation 