Opponent is the opposite of Advocate. Advocate is a synonym of Lawyer. Prosecutor is a type of Lawyer. Prosecutor is the opposite of Attorney. 
Instant is the opposite of Long. Long is related to Tail. Tail is a type of Reverse. Reverse is a synonym of Cross. 
Opponent <--Antonym--> Advocate <--Synonym--> Lawyer <--IsA-- Prosecutor <--Antonym--> Attorney 
Instant <--Antonym--> Long <--RelatedTo--> Tail --IsA--> Reverse <--Synonym--> Cross 