Defend is a synonym of Fence. Fence is a type of Fight. Fight is related to Combat. 
Apply is related to Search. Search is a type of Operation. Operation is related to Medical. Medical is related to Stroke. 
Defend <--Synonym--> Fence --IsA--> Fight <--RelatedTo--> Combat 
Apply <--RelatedTo--> Search --IsA--> Operation <--RelatedTo--> Medical <--RelatedTo--> Stroke 