Boast is related to Claim. Claim is the opposite of Back. Back is related to Swimming. 
Rock is related to Material. Material is related to Liquid. Liquid is related to Rain. 
Boast <--RelatedTo--> Claim <--Antonym--> Back <--RelatedTo--> Swimming 
Rock <--RelatedTo--> Material <--RelatedTo--> Liquid <--RelatedTo--> Rain 