Benefit is the opposite of Injure. Injure is a synonym of Hurt. Hurt is a synonym of Suffer. 
Retain is the opposite of Slip. Slip is a synonym of Case. Case is related to Judicial. 
Benefit <--Antonym--> Injure <--Synonym--> Hurt <--Synonym--> Suffer 
Retain <--Antonym--> Slip <--Synonym--> Case <--RelatedTo--> Judicial 