Casualty is a synonym of Accident. Crash is a type of Accident. Crash is related to Wave. 
Parent is related to Sheep. Sheep is related to Sleep. Sleep is a type of Accommodate. 
Casualty <--Synonym--> Accident <--IsA-- Crash <--RelatedTo--> Wave 
Parent <--RelatedTo--> Sheep <--RelatedTo--> Sleep --IsA--> Accommodate 