Pair is a synonym of Mate. Mate is related to Significant. Significant is a synonym of Crucial. Crucial is a synonym of Excellent. 
Defense is part of Trial. Defense is related to Shell. Shell is related to Sea. Sea is related to Sail. 
Pair <--Synonym--> Mate <--RelatedTo--> Significant <--Synonym--> Crucial <--Synonym--> Excellent 
Trial <--PartOf-- Defense <--RelatedTo--> Shell <--RelatedTo--> Sea <--RelatedTo--> Sail 