Killer is a type of Difficulty. Stress is a type of Difficulty. Working can cause/lead to Stress. Working requires Effort. 
Hold is a synonym of Throw. Throw is a synonym of Shy. Shy is related to Cry. Cry is related to Water. 
Killer --IsA--> Difficulty <--IsA-- Stress <--Causes-- Working --HasPrerequisite--> Effort 
Hold <--Synonym--> Throw <--Synonym--> Shy <--RelatedTo--> Cry <--RelatedTo--> Water 