Forum is a type of Meeting. Arena can be used for Meeting. you are likely to find Audience in/at/on Arena. Audience is related to Event. 
Sink is a synonym of Settle. Settle is a type of Stop. Stop is related to Traffic. 
Forum --IsA--> Meeting <--UsedFor-- Arena <--AtLocation-- Audience <--RelatedTo--> Event 
Sink <--Synonym--> Settle --IsA--> Stop <--RelatedTo--> Traffic 