Weigh is a synonym of Press. Press is related to Hard. 
Unknown is a type of Variable. Unknown is related to Mystery. Mystery is a synonym of Puzzle. Puzzle is related to Solution. 
Weigh <--Synonym--> Press <--RelatedTo--> Hard 
Variable <--IsA-- Unknown <--RelatedTo--> Mystery <--Synonym--> Puzzle <--RelatedTo--> Solution 