Sea can be used for Swim. Swim is related to Arm. Wrist is part of Arm. 
Brave is similar to Desperate. Desperate is similar to Dangerous. Dangerous is related to Vulnerable. Vulnerable is the opposite of Powerful. 
Sea --UsedFor--> Swim <--RelatedTo--> Arm <--PartOf-- Wrist 
Brave <--SimilarTo--> Desperate <--SimilarTo--> Dangerous <--RelatedTo--> Vulnerable <--Antonym--> Powerful 